ALU

Climate

Forecasting perfect storms

Science is giving us advance warning of dangerous weather combinations known as ‘compound events’. Michael Lucy reports. Original Link

Dam and blast: big hydro infrastructure needs a major rethink

Researchers call for big changes to hydropower and dam design to meet the challenges of climate change and social disruption. Nick Carne reports. Original Link

Superstars of STEM: taking the Antarctic’s temperature

The Australian state of Tasmania is a hot-bed of chilly research. Dion Pretorius reports. Original Link

Aerosol and greenhouse gas interactions determine frequency of extreme weather events

Aerosol pollution might sometimes cool things down – but that’s not good news. Nick Carne reports. Original Link

Ancient farmers survived climate change by switching crops, storing grain

Modelling tracks agricultural strategies across the Tibetan Plateau in the face of variable conditions. Samantha Page reports. Original Link

Energy transitions are nothing new but the one underway is unprecedented and urgent

The window may be closing on the opportunity to limit the damage caused by fossil fuels. Pennsylvania State University historian Brian C. Black explains. Original Link

Rising sea levels threaten Mediterranean world heritage sites

Modelling produces worrying results, but solutions can be found. Andrew Masterson reports. Original Link

Most of the Arctic’s permanent ice is gone

The polar region is now in an annual cycle of thin ice growth and melting. Nick Carne reports. Original Link

The science is clear: we have to start creating our low-carbon future today

Following the IPCC report, we have to look squarely at the goal of a zero-emissions planet, argues Australia’s Chief Scientist, Alan Finkel. Original Link

Starving bears and snowballs: talking science in a time of denial

In a world of fake news, how do scientists get their messages across? Stephen Fleischfresser reports. Original Link

In the short-term, wind power could hike global warming

Modelling finds long term positives come at the cost of more immediate negatives – but wind is still a better bet than fossil fuels. Nick Carne reports. Original Link

Jupiter and Titan findings underpin troubling news about Earth methane emissions

New modelling suggests estimates for methane’s role in global warming are on the low side. Richard A Lovett reports.  Original Link

A warming Earth might eventually copy the greenhouse effect of Venus

Modelling finds the precious equilibrium between temperature and radiation breaks down beyond a certain point, spelling big trouble. Alan Duffy reports. Original Link

Mummified penguins a sobering pointer to the future

Antarctic graveyard linked to climate patterns that are becoming more common. Nick Carne reports. Original Link

The man who went from cancer to carbon and climate

Australian marine ecologist Peter Macreadie had an early-life crisis which made him redefine his goals. He talks to Lauren Fuge. Original Link

Cold green life: the climate scientist balancing Antarctic research and sustainable living

Nerilie Abram is living the dream, and trying to ensure it doesn’t turn into a nightmare. Lauren Fuge reports. Original Link

As glaciers retreat, tsunamis may increase

Alaskan case study uncovers how glacial melt causes landslides into deep water bodies. Andrew Masterson reports. Original Link

Not-so-permafrost

Methane is already bubbling up as the Arctic thaws Original Link

Marine heatwaves set to soar

Modelling suggests damaging hot periods in oceans will increase in number and intensity. Nick Carne reports. Original Link

Geoengineering method found wanting

A proposal to reflect away incoming solar radiation may result in food supply disasters. Andrew Masterson reports. Original Link

Heatwaves and hope

Climate scientist Sarah Perkins-Kirkpatrick knows more than most about the scorching summers of the 21st century. She talks to Lauren Fuge about the future. Original Link

The California fires from above

Sparked by extreme heat, the Carr and Ferguson fires generate weather of their own. Original Link

Earth may soon become “inhospitable to current human societies”

Major study identified thresholds and tipping points that could trigger environmental disaster, even if emissions are curbed. Andrew Masterson reports. Original Link

Droughts meant the end for the Maya

Mexico’s great pre-Columbian civilisation was doomed by lack of rain. Richard A Lovett reports. Original Link

From the frontline: Escaping the Carr wildfire

Cosmos correspondent Jeff Glorfeld moved to Redding, California, just months ago. Here he reports from the tragic event that many are calling America’s wake-up call on climate change. Original Link

Cloud calculations

Complex cloud simulations may be about to get simpler. Original Link

6 ways geoengineering could fight climate change

International political efforts to curb greenhouse gas emissions are not going well: what are we to do to mitigate their warming effect? Some scientists and engineers propose a different approach, which involves dealing with gases and their effect in the atmosphere. It is called geoengineering – the large-scale intervention in the Earth’s natural systems to counteract climate change.

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Geoengineering focuses on ways to remove carbon dioxide from the atmosphere, or on offsetting warming effects by targeting the overall amount of solar energy hitting the Earth. Let’s have a look at some ideas.

REMOVING CO2

1 – PHYTOPLANKTON AND IRON

The ocean is full of living things that use photosynthesis to capture CO2, particularly single-celled algae called phytoplankton. When they die, they sink deep into the ocean, taking all that CO2 with them. Phytoplankton also need iron to grow. Some scientists have proposed increasing the ocean’s iron content, causing the phytoplankton population to increase, thereby removing more CO2.

Experiments suggest this idea, known as ocean fertilisation, can work but there are concerns that pumping iron into the sea will have unintended effects on marine ecosystems. At present large-scale ocean-fertilisation projects are banned by international treaty.

tonaquatic / Getty Images

2 – CARBON FILTERING

There are many proposals that involve removing CO2 from the atmosphere and burying it in the ground – a process called carbon sequestration – but one company in Switzerland has another idea: grab it and use it for whatever you want!

The company, called Climeworks, has developed a technology, called Direct Air Capture, that uses huge fans to suck air through a filter to which CO2 chemically bonds. When heated, the filter releases the CO2, which can then be sold for other uses, such as growing vegetables in greenhouses, making carbonated drinks or even fuel.

Such uses don’t remove CO2 from the air permanently but the technology does stop more gas being produced for commercial purposes. More permanent fixes are also available. At its CarbFix plant in Iceland, Climeworks has found a way to turn the CO2 into stone, sequestering it for millions of years.

John Thurm / Getty Images

3 – AFFORESTATION

Perhaps the least spectacular but most sensible geoengineering proposal is to simply plant trees. Lots of them. Trees use energy from sunlight to draw in carbon dioxide and water. They breathe out oxygen and use the carbon to build their trunks and roots.

It’s a good idea, for all sorts of environmental reasons, to not only stop cutting down the world’s forests but to replace the billions of trees already cut down. The feasibility of planting enough trees to offset the CO2 we are emitting by burning fossil fuels is, however, hotly disputed.

Calculations are complicated, but even the most optimistic estimates figure we would need at least a billion hectares of extra forest. That’s an area the size of Canada. According to scientists from the Potsdam Institute for Climate Impact Research, tree planting can only play a limited role – though an important one “if managed well”.

Nedomacki / Getty Images

SOLAR RADIATION MANAGEMENT

4 – STRATOSPHERIC AEROSOL INJECTION

In 1815 a volcano in Indonesia called Mount Tambora produced the largest eruption in recorded history. It ejected huge amounts of aerosols – extremely fine particles suspended in the air – into the upper atmosphere, reflecting away so much sunlight that the following year was known as ‘The Year Without a Summer’.

Now some scientists want to use this same principle to offset greenhouse gas effects. Harvard University is preparing to launch the first ever aerosol injection experiment outside a laboratory, known as the Stratospheric Controlled Perturbation Experiment (SCoPEx). A balloon will be launched high into the atmosphere. There it will release an aerosol, and scientists will observe the effect. Eventually they hope to understand the process well enough to safely use the technique on a large scale.

Fomin Sergey / Getty Images

5 – ALBEDO

Another idea is to increase the Earth’s ‘albedo’ – which is Latin for ‘whiteness’ and the measure of the amount of solar radiation the planet reflects rather than absorbs. Because whiter surfaces reflect more light than darker ones, a whiter Earth will reflect more of the Sun’s energy back into space, helping to keep temperatures cooler.

One way to do this is to make clouds brighter and whiter, an idea proposed by cloud physicist John Latham in 1990. The Marine Cloud Brightening Project at the University of Washington, Seattle, is trying to do this by spraying sea water into clouds over the ocean. The salt water will cause them to grow bigger and brighter.

Other proposals to increase the Earth’s albedo include painting houses white, planting crops that are pale and perhaps even laying out reflective sheets in deserts.

Stefan Cristian Cioata / Getty Images

6 – SPACE REFLECTORS

Particles in the stratosphere, bright clouds and painted surfaces are great, but what about doing something in space to reflect sunlight away? Could we build giant mirrors or umbrellas in orbit to keep the planet cooler?

All these ideas have been proposed, but would be so expensive that no one really thinks we could afford them.

Take the space mirrors, for example. This idea was proposed in the early 2000s by an astrophysicist named Lowell Wood, from the Lawrence Livermore National Laboratory in California. But even he thought it might be tough to do.

To be effective, 1% of the Sun’s light would have to be reflected. To achieve this, the mirrors would need to have an area of 1.6 million km2! That’s about the size of Iran.

Image Source / Getty Images

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Slow green waves: desert vegetation flows uphill

Anyone who has ever hiked through the desert knows that in dry climates vegetation grows in isolated patches, separated by bare ground. Understanding why, however, is a matter not of ecology, but mathematics.

Often, such patches are simply scattered clumps. But in some places, such as parts of Africa and Western Australia, they take the form of long arcs of dense vegetation that from space look like fingerprint whorls or waves on the ocean.

The waves can be more than 10 kilometres long and 30 metres wide, separated by as much as 100 metres of bare ground, says Mary Silber, an applied mathematician from the University of Chicago in the US, who has been studying them for several years.

And, like ocean waves, she said recently at a meeting of the Society for Industrial and Applied Mathematics (SIAM) in Portland, Oregon, these vegetation waves are also in motion, albeit very slowly.

The waves only occur, she says, on near-flat terrain, with a barely visible slope of between 0.3 and 0.8%, meaning the elevation increases by between three and eight metres every kilometre. The bands lie perpendicular to the slope, almost like contour lines.

Plants, of course, can’t move — they are literally rooted in place. But each new generation of plants slowly “colonises” bare ground on one side of the band, while older plants die off on the other. The result, says Silber, is that the bands slowly move upslope.

“[It’s] about a band width in 50 years,” she says, noting that the only way it’s been detected is by comparing modern satellite photos with aerial photos taken many decades earlier.

“It is remarkable that you can go to a paper from 1950 and go to Google Maps and find exactly the same thing, still there,” she says. “I find that incredible.”

What’s happening, her models indicate, is that the rare desert rains run off the bare patches between the bands – but not, on such gentle slopes, in gully-washing torrents. Instead, the water comes off in sheets that also remove fine material from the surface, along with light-weight litter, dead grass, and even animal faeces.

When the water hits the next downstream vegetation band, its flow is arrested and all of these nutrients, including the water itself, are caught. The effect is compounded by the fact that plants and their roots break up the soil, helping moisture to percolate into it.

One result is that the vegetation bands trap water and nutrients flowing off from upstream, giving them a significantly larger supply than the average rainfall would predict. But also, some of that moisture accumulates on the uphill side of the bands, encouraging plants to slowly grow in that direction.

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Hans Kaper, an applied mathematician at Georgetown University, Washington DC, sees this as important research, with possible relevance to global climate change.

“We want to figure out the warning signals that predict a tipping point [in climate],” he says.

When climate dries and deserts spread, he adds, plants have to adapt: “They have to share what little water there is, so they try to position themselves optimally to get the maximum water. That means they have to keep a certain distance from each other. That leads to pattern formation.”

Not that Silber’s study of vegetation bands has progressed to the point of making predictions of how, or where, deserts are spreading. At the moment, it’s confined to understanding how such vegetation bands are formed.

But figuring out the behavior of drylands ecosystems may help us understand their health and how they are changing, she and others say.

Silber’s research is available on the preprint server Arxiv.

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Superstars of STEM: making light work of heavy weather

The way we understand and apply meteorological information is ever-changing and Australian researchers are at the forefront of modelling, monitoring and predicting the weather in our region, and across the globe.

Chief Scientist of the Bureau of Meteorology, Sue Barrell, says that with increasing data, especially from satellites, and more powerful supercomputers, our ability to understand and predict the weather will transform the way we live and work.

Already we have made great leaps forward in our forecasting skill, with a seven-day forecast today better than a three-day forecast 30 years ago.

“A small but powerful example of this is on the oil rigs at sea,” says Barrell.

“Often the people working on these rigs would need to be evacuated in case of a chance of dangerous weather, which would cost the company hundreds of thousands or even millions of dollars in evacuation costs and lost production.

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“With more accurate predictions of tropical cyclones, the oil rig operators can more accurately assess the risks and avoid unnecessary evacuations, saving money for the business and for consumers.”

Barrell says a major focus for the Bureau is working more closely with customers to ensure that forecasts more directly assist them in their decision-making. “It’s not just what the weather will ‘be’ that’s important, but what the weather will ‘do’.”

In November 2016, one of the deadliest asthma events in Australia’s recent history left 10 people dead and thousands with respiratory problems. Health services and hospitals in the cities of Melbourne and Geelong, in the state of Victoria, were caught by surprise and unable to respond effectively.

Barrell says that in the wake of such a major event, the challenge is to develop systems that will help minimise future impacts, and the Bureau of Meteorology is working hard to achieve that goal.

What made this 2016 storm different was the combination of several critical factors – a wet spring across the ryegrass areas to the north and west of Melbourne, the first really hot day since the previous summer, high humidity and a series of violent storms with ferocious winds, which meant airborne pollen was crushed into tiny fragments.

Usually, pollen particles are big enough to be caught by the nasal passages, which can cause a bit of discomfort, scratchiness, a running nose and sneezing, but won’t usually be life-threatening.

Beth Ebert, who has led the Bureau’s work in this area, says that pollen was given more potency than usual thanks to its smaller size.

“A thunderstorm is a bit like a broom, which sweeps up the pollen and dust and hurtles it around,” she explains.

“Because the pollen was moist and breakable, we think the storm caused it to shatter into smaller pieces; small enough to bypass the nasal passages and go straight to the lungs.”

Barrell says the next stage involves collaborating with other scientists and health specialists to learn more and translate that knowledge into action.

“As the Bureau’s services improve, the demand for more accurate, more local, more immediate weather information and forecasts is constantly increasing,” she explains.

“The Bureau is working in partnership with governments, emergency managers and industry to ensure these improvements translate to improved safety, productivity and well-being for Australians.

“The potential is big, and Australia is at the forefront of getting our weather predictions and monitoring to those who will benefit most from them.”


Sue Barrell is among 30 Superstars of STEM featured in this weekly series prepared by Science & Technology Australia (STA). To learn more about the program, visit the STA website.

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How clouds complicate global warming

Clouds are wispy evanescent things, beloved of poets and daydreamers. They may also determine whether civilisation as we know it survives the 21st century.

Depending on how clouds react to global warming, they could cool or cook the planet. But, so far, we haven’t been able to predict which way they will swing. That’s a big problem for our ability to prepare for what’s coming.

“When we look into the future, the most uncertain part of the climate models is what will happen to the clouds,” says Christian Jakob, an atmospheric scientist at Monash University. “It’s a devilishly intricate problem.”

Understanding clouds, circulation and climate sensitivity is one of several grand challenges that the Swiss-based World Climate Research Programme (WCRP) is focusing on. The programme brings together scientists from all over the world to tackle big questions in climate science, and it considers cloud feedback “the intellectual and experimental challenge of our lifetime”.

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Clouds depend on a huge number of processes that act on scales from the sub-millimetre-sized world of water droplets and ice crystals to the kilometres-wide spread of a thunderstorm and beyond. Limits on computing power, however, mean that climate models are often ‘low res’. Their blocky simulations chop the planet up into 100 km square pixels.

“So what we try to do is build mathematical models of how clouds work in one of those 100 by 100 kilometre areas,” says Jakob. These small-scale results are then averaged out and plugged into the larger-scale models.

When it comes to warming, clouds acts in three ways. They act like silvery shields reflecting away incoming sunlight; they act like insulators trapping heat on the planet (recall how much cooler it gets on a cloudless night); and they act like radiators sending heat out into space. Whether a cloud acts more like a shield, a blanket or a radiator depends on where it lies and what it’s made of.

And here things get diabolically complex. Though they are a small piece of the overall climate puzzle, solving the behaviour of clouds is a problem with many, many moving parts.

“The most uncertain part of the climate models is what will happen to the clouds.”

It’s understood that low clouds tend to radiate more heat back to space, because they are warmer. High clouds are cooler, and radiate less heat. Bottom line: low clouds will help cool the planet; high clouds will push temperatures further up.

Worryingly, there are signs that high clouds are getting higher. But altitude is just the first entry on this list of moving parts.

If a warming climate makes clouds more watery and less icy, they will become more shiny and help cool things down.

At the same time, changing weather patterns may move clouds around the globe. For instance, banks of low, reflective cloud are already shifting away from middle latitudes towards the poles, which leaves less shielding against the brightest equatorial light. The net effect is to speed up warming.

Even the shape of the water droplets or ice crystals in the cloud influence their climate impact. “It can be hexagons, it can be needles, it can be all sorts of things. It matters,” explains Jakob.

Beyond water molecules, the aerosol particles that trigger the condensation of droplets are another key variable. “That’s where chemistry comes in,” says Robyn Schofield, a chemist at the University of Melbourne. “A sulfur particle or sea salt is pretty good at taking water up. Black carbon is less good.”

Aerosols can affect both the amount of cloud and the size of the droplets inside it. Smaller droplets reflect more light, making for better shields.

(click image to expand)

Adapted from a Scientific American illustration

To gather data on cloud chemistry, Schofield’s team has built a mobile lab in a shipping container that goes by the acronym AIRBOX (Atmospheric Integrated Research facility for Boundaries and OXidative experiments).

Last summer, aboard the CSIRO ship RV Investigator, the lab headed south to a data desert: the Southern Ocean. “That’s the area where there is the most uncertainty about clouds and aerosols,” says Schofield. The study was part of a major US and Australian collaboration.

“The US brought in their Gulfstream V research plane to sample clouds, the RV Investigator was out there with cloud radar and lidar. There was some equipment on Macquarie Island and on the icebreaker Aurora Australis,” says Steve Siems of Monash University, who participated in the effort from Hobart. “We’re overwhelmed. We’ll be looking at these data for the next five years.”

The new data will help constrain the moving parts in our models of cloud formation and, in due course, narrow down the size of the likely global temperature increase.

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At issue is climate sensitivity, which measures how much the temperature changes if the amount of carbon dioxide (CO2) in the atmosphere doubles. In 2014 the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) estimated this number somewhere between 1.5 and 4.5°C. This huge range comes down almost entirely to the effect of clouds.

“We haven’t really uncovered any other possible major uncertainty,” says Steven Sherwood, a climate scientist at the University of New South Wales.

By amplifying warming or reining it in, clouds could make the difference between a 2°C increase – where sea levels rise a metre or more and deadly heatwaves are predicted – and a truly catastrophic 4.5°C – which, according to the IPCC, means widespread extinctions, global food supplies at risk and many parts of the planet too hot to live in.

The latest data suggest clouds will amplify warming, though not as severely as some models had implied.

That means more than 3°C of warming by 2100 if the world’s countries make the emissions cuts promised in the Paris Agreement, which is well beyond the agreement’s target of less than 2°C.

But however much CO2 we put into the atmosphere, the precise effect will depend on clouds. To get a better sense of the details, we still have quite a wait: the next IPCC assessment is due out in 2021.

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Major wind shifts emerge from smaller changes

Scientists have solved the riddle of strong winds that circle the planet in the upper atmosphere, and why they reverse their direction seemingly at random.

The new model could not only help atmospheric scientists understand the weather on Earth, but could apply to fluid flow in the planet’s interior, and in the atmospheres of stars and gas giants such as Jupiter, and the magnetic fields they generate.

Above the storms and changeable winds we live in, there is a much more stable layer known as the stratosphere. In this zone, more than 10 kilometres up, there are strong, steady winds that blow in the same direction for months on end before mysteriously reversing direction. The change is unrelated to any seasonal effects.

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The wind is known as the Quasi-Biennial Oscillation because it switches direction and then returns to its original direction on average every 26 months. The individual reversals occur anywhere between 11 months and 17 months apart – behaviour that a team led by Louis-Alexandre Couston from Aix Marseille University in France has now managed to simulate in computer models.

The surprise is that the long-term behaviour is the result of energy injected from storms in the troposphere, the turbulent zone below the stratosphere, in short and seasonal bursts.

“You have turbulence in the troposphere, cyclones and storms that try to push up into the stratosphere, and they create waves there,” explains Couston.

The group set up their model, reported in the journal Physical Review Letters, to explore the effect of the waves, using 10 minute increments.

With a good stretch of supercomputer time at his disposal, Couston and colleagues decided to run the simulation for a long time to see what happened.

To his surprise the waves didn’t just pass through the stratosphere, but, over a period of many months, began to build up a constant flow direction.

If easterly winds happened to initially dominate the troposphere, Couston found an easterly flow began in the stratosphere. Once moving, the flow picked up energy more efficiently from extra easterly waves than from westerly ones, building the overall flow direction.

The reversal came when the energy in the easterly waves had been exhausted, and westward flows began to take over again.

“The stratosphere is working in layers – not all of it is moving to the east,” Couston says.

“The change of direction comes from the top of the stratosphere, even though the waves are coming from the bottom. The top layer starts changing direction, and then the bottom layer follows.”

The interaction between the two atmospheric layers appears to be mutual. The troposphere seems to be affected by the stratospheric flows, too. Work at the UK meteorological office linked the Quasi-Biennial Oscillation to irregular weather patterns in UK.

Couston hopes the new model could also help understand the dynamics of the sun, in which the set up is reversed, with a turbulent layer on the outside and a more stable one inside it.

As to whether the turbulence in the Earth’s liquid interior could generate reversing flows linked to reversals in the Earth’s magnetic field, Couston is cautious.

“It’s an open question. This is very preliminary, but it is not out of the question that it is influencing it in some way,” he says.

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Long-range rain connections

Winter rainfall in the south-western United States is connected to sea surface temperatures six months earlier near New Zealand, according to new research published in Nature Communications.

This long-distance link, known as a teleconnection, begins when heating or cooling of the sea surface temperature in the south-western Pacific Ocean causes changes in atmospheric circulation between the equator and a latitude about 30 degrees south. This circulation affects the weather east of the Philippines, which in turn causes the jet stream to become weaker or stronger in the northern hemisphere, and the jet stream directly influences the amount of rain coming off the Pacific onto California between November and March.

So the rainstorm shown above, sweeping across Arizona, owes its genesis in some part on the warmth of the water around New Zealand.

This connection appears to be growing stronger in recent decades, and may be a useful tool for predicting rainfall as traditional indicators such as El Nino variations become less reliable.

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Antarctica has lost three trillion tonnes of ice in 25 years. Time is running out for the frozen continent

Antarctica lost 3 trillion tonnes of ice between 1992 and 2017, according to a new analysis of satellite observations. In vulnerable West Antarctica, the annual rate of ice loss has tripled during that period, reaching 159 billion tonnes a year. Overall, enough ice has been lost from Antarctica over the past quarter-century to raise global seas by 8 millimetres.

What will Antarctica look like in the year 2070, and how will changes in Antarctica impact the rest of the globe? The answer to these questions depends on choices we make in the next decade, as outlined in our accompanying paper, also published today in Nature.

Our research contrasts two potential narratives for Antarctica over the coming half-century – a story that will play out within the lifetimes of today’s children and young adults.

While the two scenarios are necessarily speculative, two things are certain. The first is that once significant changes occur in Antarctica, we are committed to centuries of further, irreversible change on global scales. The second is that we don’t have much time – the narrative that eventually plays out will depend on choices made in the coming decade.

Change in Antarctica has global impacts

Despite being the most remote region on Earth, changes in Antarctica and the Southern Ocean will have global consequences for the planet and humanity.

For example, the rate of sea-level rise depends on the response of the Antarctic ice sheet to warming of the atmosphere and ocean, while the speed of climate change depends on how much heat and carbon dioxide is taken up by the Southern Ocean. What’s more, marine ecosystems all over the world are sustained by the nutrients exported from the Southern Ocean to lower latitudes.

From a political perspective, Antarctica and the Southern Ocean are among the largest shared spaces on Earth, regulated by a unique governance regime known as the Antarctic Treaty System. So far this regime has been successful at managing the environment and avoiding discord.

However, just as the physical and biological systems of Antarctica face challenges from rapid environmental change driven by human activities, so too does the management of the continent.

Antarctica in 2070

We considered two narratives of the next 50 years for Antarctica, each describing a plausible future based on the latest science.

In the first scenario, global greenhouse gas emissions remain unchecked, the climate continues to warm, and little policy action is taken to respond to environmental factors and human activities that affect the Antarctic.

Under this scenario, Antarctica and the Southern Ocean undergo widespread and rapid change, with global consequences. Warming of the ocean and atmosphere result in dramatic loss of major ice shelves. This causes increased loss of ice from the Antarctic ice sheet and acceleration of sea-level rise to rates not seen since the end of the last glacial period more than 10,000 years ago.

Warming, sea-ice retreat and ocean acidification significantly change marine ecosystems. And unrestricted growth in human use of Antarctica degrades the environment and results in the establishment of invasive species.

Under the high-emissions scenario, widespread changes occur by 2070 in Antarctica and the Southern Ocean, with global impacts.

Under the high-emissions scenario, widespread changes occur by 2070 in Antarctica and the Southern Ocean, with global impacts.

Rintoul et al. 2018

In the second scenario, ambitious action is taken to limit greenhouse gas emissions and to establish policies that reduce human pressure on Antarctica’s environment.

Under this scenario, Antarctica in 2070 looks much like it does today. The ice shelves remain largely intact, reducing loss of ice from the Antarctic ice sheet and therefore limiting sea-level rise.

An increasingly collaborative and effective governance regime helps to alleviate human pressures on Antarctica and the Southern Ocean. Marine ecosystems remain largely intact as warming and acidification are held in check. On land, biological invasions remain rare. Antarctica’s unique invertebrates and microbes continue to flourish.

Antarctica and the Southern Ocean in 2070, under the low-emissions (left) and high-emissions (right) scenarios. Each of these systems will continue to change after 2070, with the magnitude of the change to which we are committed being generally much larger than the change realised by 2070.

Antarctica and the Southern Ocean in 2070, under the low-emissions (left) and high-emissions (right) scenarios. Each of these systems will continue to change after 2070, with the magnitude of the change to which we are committed being generally much larger than the change realised by 2070.

Rintoul et al. 2018

The choice is ours

We can choose which of these trajectories we follow over the coming half-century. But the window of opportunity is closing fast.

Global warming is determined by global greenhouse emissions, which continue to grow. This will commit us to further unavoidable climate impacts, some of which will take decades or centuries to play out. Greenhouse gas emissions must peak and start falling within the coming decade if our second narrative is to stand a chance of coming true.

If our more optimistic scenario for Antarctica plays out, there is a good chance that the continent’s buttressing ice shelves will survive and that Antarctica’s contribution to sea-level rise will remain below 1 metre. A rise of 1m or more would displace millions of people and cause substantial economic hardship.

Under the more damaging of our potential scenarios, many Antarctic ice shelves will likely be lost and the Antarctic ice sheet will contribute as much as 3m of sea level rise by 2300, with an irreversible commitment of 5-15m in the coming millennia.

The ConversationWhile challenging, we can take action now to prevent Antarctica and the world from suffering out-of-control climate consequences. Success will demonstrate the power of peaceful international collaboration and show that, when it comes to the crunch, we can use scientific evidence to take decisions that are in our long-term best interest.

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The choice is ours.

This article was originally published on The Conversation. Read the original article.

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Africa’s ancient baobabs are dying

In recent years, many of the largest and oldest African baobab trees have either died or have lost their oldest sections, new research reveals.

The study, published in the journal Nature Plants, suggests that significant changes in regional climate could be to blame.

The African baobab (Adansonia digitata) is by far the largest and longest living flowering tree in the world. Widespread throughout savannah regions in Africa, baobabs can achieve girths of more than 35 metres, wood volumes of 500 cubic metres, and reach ages of more than two millennia.

Until recently, the growth patterns and architecture of baobabs were poorly understood. Dissecting a dead, collapsed structure doesn’t quite reveal what grew when. Moreover, tree ring analysis can’t provide a clear picture of a baobab’s growth history, because baobabs have hollow cores and their tree rings tend to be either non-existent or too faint to accurately count.

Over the past 13 years, Adrian Patrut of Babeş-Bolyai University in Romania, together with colleagues in South Africa and the US, used radiocarbon dating of multiple sections of live baobabs to reveal that these trees have an incredibly complex structure.

They found that baobabs begin growth as a single-stemmed plant, but over time they periodically produce new stems, much like other trees grow new branches. Eventually, these stems form a ring that fuses together around a hollow centre. No other known tree species does this.

Between 2005 and 2017, Patrut and colleagues surveyed 60 of the largest and oldest African baobab specimens known, all in southern Africa. They observed a disturbing pattern: eight of the 13 oldest treees, and five of the largest six, had either died entirely, or lost their oldest stems.

This included a baobab named ‘Panke’ in Zimbabwe. Beginning in 2010, over the course of a year or so, Panke’s stems collapsed one by one. Radiocarbon dating revealed the tree had been approximately 2450 years old. It had been the oldest known flowering plant in existence.

In 2016, another exceptional example died. The Chapman baobab in Botswana had three generations of stems ranging from 500 to 1400 years old, all of which died in close succession that January.

Meanwhile, numerous others, including the massive, nearly-1000-year-old Platland baobab in South Africa, have lost their oldest stems, often accounting for half the tree or more in the process.

These incidents are part of an unprecedented rise in natural deaths of mature baobabs. There are no signs of an epidemic.

“We suspect that the demise of monumental baobabs may be associated at least in part with significant modifications of climate conditions that affect southern Africa in particular,” say Patrut and his colleagues in the new paper.

These changes in climate include a severe El Niño–linked drought in 2015 and 2016, as well as a rise in near-surface temperatures over the past five decades at more than twice the global rate.

Patrut and colleagues propose that further research into the interaction between baobabs and their changing regional climate may help explain why so many older baobabs are now struggling to survive.

Original Link

Across the world, cyclones are creeping more slowly

Sluggish superstorms like Hurricane Harvey – which loitered over eastern Texas for four days in 2017, dumping up to a metre of rain and causing unprecedented floods – may be commonplace in the future, if a newly identified 70-year slowdown in tropical cyclone speeds continues.

In a climate change-inspired study of tropical cyclones around the world, published in the journal Nature, James Kossin from the US National Oceanic and Atmospheric Administration (NOAA) found an average 10% drop since 1949 in “translation speed”, or how fast the storm moves from place to place.

All other things being equal, according to the paper, a slower storm has more time to dump rain on a given location and is more likely to cause flooding.

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“[Translation speed] is not something a lot of people have looked at,” says Kevin Walsh, a cyclone expert at the University of Melbourne in Australia. “This will spark a lot of effort to find out what’s going on and explain it physically.”

Earlier research had shown that tropical cyclones are gradually becoming more intense and moving away from the equator toward the poles, in changes that largely agree with what climate models predict will happen as the world warms.

This study began with the idea that rising temperatures might also have affected how fast tropical cyclones move around. Tropical cyclones form around a region of low air pressure over a warm ocean, but once formed they are pushed around by bigger currents of air.

“Global warming causes changes in the global wind patterns,” says Kossin. “Since tropical cyclones are mostly just carried along in these winds, those changes should show up in their translation speed.”

Large-scale atmospheric circulation in the tropics during the summer cyclone season appears to be slowing down, he says, so finding evidence that cyclones are also moving slower wasn’t entirely surprising.

“But I was surprised at how large and significant a signal it was,” he adds.

Sifting through decades of records from around the world, Kossin found tropical cyclones slowing down everywhere they occur except the northern Indian Ocean. Particularly large drops occurred along the western edge of the North Pacific (30%), the west of the North Atlantic (20%) and around north-eastern Australia (19%).

While the evidence for the drop is clear, the physical mechanism behind it – and any connection to global warming – is still up in the air.

“This will hopefully galvanize new research that explores the cause of the slowdown,” says Kossin. “But until then, we can only speculate and say that the findings are consistent with what might be expected in a warming world.”

At this stage, the results are unlikely to change anyone’s cyclone forecasts.

“Global warming presents a very real threat of flooding potential from tropical cyclones,” says Thomas Loridan, a co-founder of the Australian company Reask, based in Australia, which studies climate-related risk for the insurance industry. In Australia, he says, slower-moving cyclones are most likely to affect the Queensland coast: “Increased flooding risk can be expected all the way down to Brisbane.”

However, precisely because Kossin’s research is consistent with theoretical expectations for a warming world, it won’t yet affect projections for the future.

“The physical arguments [for cyclones slowing down] are very strong and well documented,” says Loridan. “The evidence from the data doesn’t necessarily provide us with a lot of additional confidence.”

Kossin stands by the work, arguing that it adds plenty to our confidence in the theory of human-induced global warming and the broader climatic changes it is driving.

“It’s not enough to just expect something to be true,” he says. “Someone needs to go in and do the analysis.”

Original Link

“Stranded” fossil fuel assets may prompt $4 trillion crisis

The world could be heading for fiscal havoc on a scale not seen since the 2008 financial crisis, erasing as much as $US4 trillion from the global economy, with fossil fuel industries at the centre of the upheaval, and the United States, Russia and Canada tipped as big losers, according to a new study published in the journal Nature Climate Change.

The study is by an international team of scientists led by Jean-Francois Mercure, from Radboud University, The Netherlands, and includes researchers from the University of Macau and Britain’s Cambridge University. It blames several factors for the impending economic slide.

Some of the world’s biggest economies rely on fossil fuel production and exports, just as the movement towards energy efficiency, low-carbon, renewable energy production and various national climate policy initiatives substantially reduce global demand for coal, oil and gas.

Meanwhile, according to reports by bodies such as the International Energy Agency, investment in fossil fuel ventures is surging, and production remains high, even while interest in renewable energy also grows.

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The result, the researchers say, is a global glut of “stranded fossil fuel assets”, where net carbon importers such as China and the European Union emerge as “winners”.

The study cites a 2015 report by the Bank of England’s Prudential Regulation Authority that separates fossil fuels into two groups:

Tier 1 includes coal, oil and gas extraction companies, and conventional utilities; as well as firms that are energy-intensive, which might be affected indirectly via an increase in energy costs.

Tier 2 includes chemicals, forestry and paper, metals and mining, construction and industrial production.

“Between them, these two tiers of assets account for around a third of global equity and fixed-income assets,” the bank’s report says.

The Paris Agreement, the study notes, aims to limit the increase in global average temperature to “well below two degrees Celsius above pre-industrial levels”, which means a portion of existing reserves of fossil fuels and production capacity will remain unused, becoming stranded.

If investors assume that these reserves will be commercialised, the stocks of listed fossil fuel companies may be overvalued. “This gives rise to a ‘carbon bubble’, which has been emphasised or downplayed by reference to the credibility of climate policy”, the Mercure study says.

It says stranding results from an ongoing technological transition, which remains robust even if big fossil fuel producers – the US, for example – fail to adopt climate mitigation policies.

The economic impact on big fossil fuel producers would be aggravated by such failures because their exposure to stranding would be increased as global demand for their products decreases, potentially amplified by a likely asset sell-off by lower-cost fossil fuel producers and new climate policies.

For importing countries, the report says, stranding has moderate positive effects on gross domestic product and employment levels.

The researchers say their conclusions support the existence of a carbon bubble that, “if not deflated early, could lead to a discounted global wealth loss of $US1 trillion to $US4 trillion, a loss comparable to the 2008 financial crisis”. However, they say further economic damage from a potential bubble burst could be avoided by “decarbonising” early.

They acknowledge that the existence of a carbon bubble has been questioned on grounds of credibility or of timing of climate policies, which would explain investors’ relative confidence in fossil fuel stocks and the projected increase in fossil fuel prices until 2040. “But there is evidence that climate mitigation policies may intensify in the future,” they note.

A 2016 report by the London School of Economics and Political Science, and the Grantham Research Institute on Climate Change and the Environment, cited by this new study, says that more than 75% of global emissions from 99 countries surveyed are subject to economy-wide emissions-reduction or climate policy schemes.

Moreover, Mercure and his colleagues say, the ratification of the Paris Agreement and its reaffirmation at the 22nd Conference of the Parties (COP22) in 2016 have added momentum to climate action, “despite the position of the new US administration”.

“Furthermore,” the researchers write, “low fossil fuel prices may reflect the intention of producer countries to sell out their assets – that is, to maintain or increase their level of production despite declining demand for fossil fuel assets.”

But irrespective of whether new climate policies are adopted, global demand for fossil fuels is already slowing in the current technological transition, they say. The question then is whether, under the current pace of low-carbon technology diffusion, fossil fuel assets are bound to become stranded, owing to the growth in renewable-energy use, improved fuel efficiency in transport, and growing acceptance of electric-powered transport vehicles.

“Indeed, the technological transition currently under way has major implications for the value of fossil fuels, due to investment and policy decisions made in the past,” Mercure and colleagues conclude.

“Faced with stranded fossil fuel assets of potentially massive proportions, the financial sector’s response to the low-carbon transition will largely determine whether the carbon bubble burst will prompt a 2008-like crisis.”

Original Link

If it’s not one thing, it’s another: the challenge of compound weather events

The deadly Russian wildfires of 2010, the Brisbane floods of 2011 and the inundation of New York by Hurricane Harvey in 2012 were all “perfect storms”, devastating combinations of weather and climate conditions that no-one saw coming.

“Compound events” such as these – where drought amplifies a heatwave, or one storm comes hard on the heels of another – could have been foreseen, according to one group of climate scientists, who argue that most analysis of the hazards of climate change underestimates the real risks.

In a paper published in the journal Nature Climate Change, the group – made up of Swiss, Dutch, American and Australian researchers – make the case that “most major weather and climate-related catastrophes are caused by compound effects”, and call for turning climate risk projections upside down.

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After disastrous events such as fires and floods, says Michael Leonard of the University of Adelaide in South Australia, one of the authors of the paper, people sometimes want to think they were unavoidable:

“You’ll often hear phrases like ‘We didn’t see it coming’,” he says, “when, actually, maybe we could have seen it coming. I guess there’s a public need for people to excuse themselves a bit, but from a professional point of view planners and modellers can do better.”

Climate scientists have only begun coming to grips with the problem of compound events over the last half-dozen years. As recently as 2012, a 500-page report by the Intergovernmental Panel on Climate Change (IPCC) on the risks of extreme events spent barely half a page on the topic.

No-one really knew how to approach the problem, Leonard says. There were too many variables, and cross-referencing every possible set of conditions seemed impossible: “It was in the too-hard basket.”

By 2014, however, he and some colleagues had put together a framework for thinking about compound events and the risks they pose.

“What’s happened traditionally is a top-down approach,” he explains.

“You do some climate modelling and see that temperature or rainfall is going to change, and then you spread that out over some region and see what’s going to happen.”

The top-down approach can miss connections, however. A single day of heavy rainfall might not cause a flood, but two days in the same week might, or simultaneous heavy rainfalls in different parts of the same water catchment, especially if the soil is already wet.

Leonard proposed a bottom-up approach. “You have to start with the end users,” he says, such as emergency services. “You ask what the impact is [of fires or floods], and what are the circumstances that can lead to it. And you work back from there.”

Often, he says, it’s a question of the scale on which the problem is viewed.

“Say you have a single high-pressure [weather] system,” he explains.

“You might have drought conditions, where there is a lot of heat stress, and a heat wave, and then on top of that some bushfires in the same region.

“You’ve got landowners who are stretched by the burdens of maintaining farm under drought conditions, then simultaneously there’s a nursing home stressed by the heatwaves, and then bushfire conditions that require evacuation. Those are three very different types of impact, but they all come from the same underlying drivers.”

In this case, he argues, a government agency or emergency service should take a large enough view to be aware that these three things are likely to happen together, and plan accordingly.

Zooming out even further, even an enormous event like the hot Russian summer of 2010 – which sparked vast wildfires and led to more than 55,000 deaths – was only part of a large compound weather event that also caused enormous flooding in the Indus valley, affecting tens of millions of people in Pakistan.

In principle, an international agency might one day be able to plan for the risk of such events, though that is a long way off.

“If you’re just doing Pakistani regional response, you wouldn’t care about heatwave in Russia, and vice versa,” he says.

Awareness of the significance of compound events is percolating through the scientific community. While the IPCC’s fifth Assessment Report, the major document summarising the state of the world’s climate-change knowledge, published in 2014, made no mention of compound events, things are already changing.

Kathleen McInnes is a climate scientist at Australian research body CSIRO who is working on the IPCC Special Report on the Oceans and Cryosphere in a Changing Climate, one of three special reports to be published before the next full Assessment Report.

“These special reports are initiated to address gaps in what’s been assessed in IPCC reports before,” she says.

The report she is working on will not only take compound events into account, but move a step further to look at how one extreme event can reduce people’s protection against others.

“It’s not just that the hazards can be compound – like storm surge combined with rain – the vulnerability and exposure can also be compound,” says McInnes, giving the example of a storm that washes sand away from a beach.

“If you get a second storm a week later, the beach hasn’t recovered so the waves come right in and start attacking the properties behind.”

Compound event analysis will also be incorporated into the IPCC’s sixth report, due to be published in 2022.

At the same time, Leonard and colleagues are calling for awareness of compound event risks beyond the scientific community, in practical planning for the future.

“People can compartmentalise things too easily, and rationalise that it’s too hard to think of everything that can happen with everything else,” he says.

“We’re calling for greater scrutiny. We should actually look at some of those dependencies and do a better job.”

Original Link

When the wind slows

The wind isn’t what it used to be. Scientists say surface wind speeds across the planet have fallen by as much as 25% since the 1970s. The eerie phenomenon – dubbed ‘stilling’ – is believed to be a consequence of global warming, and may impact everything from agriculture to the liveability of our cities. It has taken more than a decade for scientists to get a handle on stilling, a term coined by Australian National University ecohydrologist Michael Roderick in 2007.

Roderick had spent years studying a 50-year decline across Europe and North America of a climate metric called pan evaporation. It measures the rate at which water evaporates from a dish left outside. With his colleague biophysicist Graham Farquhar, he found the cause: the sunlight had dimmed due to air pollution. Less light equals slower evaporation.

In 2002, after publishing the explanation in the journal Science, Roderick received a query from Roger Beale, the head of Australia’s federal department for the environment. Was pan evaporation also declining in Australia? “To my embarrassment,” Roderick recalls, “I had to say I didn’t know, because I’d never looked.”

Two years later, he had an answer: the pan evaporation rate was also falling in Australia. It was puzzling, however, as air pollution levels on the continent were lower than those of Europe or North America.

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Roderick went back to basics. The rate of evaporation depends on four factors: air temperature, humidity, the amount of solar radiation and wind speed. After another three years of combing through meteorological records, he had pinned down the culprit: “To my absolute surprise, we found the main reason for the drop in Australia was less wind – and by a lot.”

Roderick unearthed other local studies from around the world with similar findings, but till then no one had joined the dots.

He teamed up with Tim McVicar, a hydrologist at Australia’s national science agency, the CSIRO, who was looking for global wind patterns and their effects on evaporation. In 2012 this team – led by McVicar – compiled results from almost 150 regional studies to show stilling was taking place across much of the world.

In Australia in the 1970s, average wind speed a couple of metres above the ground was 2.2 metres per second: in 2017 it was 1.6 metres per second.

Over landmasses from as far north as Svalbard, 1,050 km from the North Pole, to as far south as the coast of Antarctica, “observations show that wind is stilling”, McVicar says.

Conversely, the wind is getting faster around the poles and in certain coastal areas. In a perplexing twist, ocean winds also appear to be accelerating.

Several explanations have been proposed for the stilling.

Robert Vautard, who studies climate change at France’s National Centre for Scientific Research, has a benign answer for some of the change: more vegetation, spurred by rising temperatures and carbon dioxide levels. It increases ‘surface roughness’, which slows the wind.

The planet’s rising temperatures are another likely culprit.

One projected consequence of global warming is expansion of the ‘Hadley cell’, a planet-girdling double doughnut of atmospheric circulation in which warm air rises near the equator, loops towards the poles, cools and falls to the surface at around 30 or 40 degrees latitude, then heads back to its origin. This circulation, combined with the Coriolis effect of Earth’s rotation, causes the consistent easterly trade winds found in the tropics and the prevailing westerlies of the middle latitudes. An expanding Hadley cell means many common storm tracks are slipping towards the poles, taking their high winds – and associated rainfall – away from the temperate regions.

Roderick takes a more telescopic view: air movements are powered by differences in temperature at different places. The bigger the difference between warm and cold air, the stronger the wind. One effect of global warming is to flatten those differences. The poles are warming faster than the equator, winters are warming faster than summers, and nights warming faster than days. “Everything becomes more uniform,” Roderick says.

What does the drop in wind speed mean? The decrease in evaporation has immediate implications for the precision calculations used in modern irrigation, and more complex effects on rainfall patterns.

While less evaporation may be good for some plants in arid areas, stilling may make others less able to disperse wind-blown seed to suitable new habitats, and hence less resilient to climate change.

Less wind could also hurt city-dwellers. In what may be a taste of things to come, the winter of 2016/17 saw Europe becalmed, leading to smog so bad that Paris banned cars for six days, and the city of Skala in Poland briefly overtook Beijing atop the world’s air-pollution tables.

Potential effects on wind power are another area of concern, though there does not appear to be anything to worry about in the short term. Stilling has so far been detected only at heights up to 10 metres, while turbines harvest their energy 50 to 150 metres above the ground.

“We certainly haven’t seen anything that looks like stilling,” says Keith Ayotte, the chief scientist of Australian wind power outfit WindLab, who monitors more than 100 sites across the world where the company has turbines.

Though these higher-altitude winds will change over the 21st century, Vautard has used climate simulations to project the effect on total wind power available across Europe is unlikely to be more than 5%. One difficulty with prediction is a lack of observations. As McVicar notes, accurate and consistent measurements only exist “for the past 40 or 50 years”.

Cesar Azorin-Molina, a climate scientist at the University of Gothenburg in Sweden, has embarked on an EU-funded archival project with the effortful acronym STILLING: “TowardS improved undersTandIng of the worLdwide decline of wind speed in a cLImate chaNGe scenario.”

His mission is “rescuing historical wind speed data” like logbooks from Ponta Delgada in the Azores and Blue Hill Observatory in the US that go back more than a century. The age of anemometers – the devices that measure wind speed – can affect readings but, by compiling a single set of quality-controlled data, Azorin-Molina hopes to determine whether stilling is purely a recent phenomenon or if similar declines have happened in the past.

For McVicar, the stilling of the planet’s winds is a reminder that global warming has multiple and unpredictable flow-on effects. “We’re dealing with climate change, not just rising temperatures.”

Original Link

The wind is slowing down

The wind isn’t what it used to be. Scientists say surface wind speeds across the planet have fallen by as much as 25% since the 1970s. The eerie phenomenon – dubbed ‘stilling’ – is believed to be a consequence of global warming, and may impact everything from agriculture to the liveability of our cities. It has taken more than a decade for scientists to get a handle on stilling, a term coined by Australian National University ecohydrologist Michael Roderick in 2007.

Roderick had spent years studying a 50-year decline across Europe and North America of a climate metric called pan evaporation. It measures the rate at which water evaporates from a dish left outside. With his colleague biophysicist Graham Farquhar, he found the cause: the sunlight had dimmed due to air pollution. Less light equals slower evaporation.

In 2002, after publishing the explanation in the journal Science, Roderick received a query from Roger Beale, the head of Australia’s federal department for the environment. Was pan evaporation also declining in Australia? “To my embarrassment,” Roderick recalls, “I had to say I didn’t know, because I’d never looked.”

Two years later, he had an answer: the pan evaporation rate was also falling in Australia. It was puzzling, however, as air pollution levels on the continent were lower than those of Europe or North America.

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Roderick went back to basics. The rate of evaporation depends on four factors: air temperature, humidity, the amount of solar radiation and wind speed. After another three years of combing through meteorological records, he had pinned down the culprit: “To my absolute surprise, we found the main reason for the drop in Australia was less wind – and by a lot.”

Roderick unearthed other local studies from around the world with similar findings, but till then no one had joined the dots.

He teamed up with Tim McVicar, a hydrologist at Australia’s national science agency, the CSIRO, who was looking for global wind patterns and their effects on evaporation. In 2012 this team – led by McVicar – compiled results from almost 150 regional studies to show stilling was taking place across much of the world.

In Australia in the 1970s, average wind speed a couple of metres above the ground was 2.2 metres per second: in 2017 it was 1.6 metres per second.

Over landmasses from as far north as Svalbard, 1,050 km from the North Pole, to as far south as the coast of Antarctica, “observations show that wind is stilling”, McVicar says.

Conversely, the wind is getting faster around the poles and in certain coastal areas. In a perplexing twist, ocean winds also appear to be accelerating.

Several explanations have been proposed for the stilling.

Robert Vautard, who studies climate change at France’s National Centre for Scientific Research, has a benign answer for some of the change: more vegetation, spurred by rising temperatures and carbon dioxide levels. It increases ‘surface roughness’, which slows the wind.

The planet’s rising temperatures are another likely culprit.

One projected consequence of global warming is expansion of the ‘Hadley cell’, a planet-girdling double doughnut of atmospheric circulation in which warm air rises near the equator, loops towards the poles, cools and falls to the surface at around 30 or 40 degrees latitude, then heads back to its origin. This circulation, combined with the Coriolis effect of Earth’s rotation, causes the consistent easterly trade winds found in the tropics and the prevailing westerlies of the middle latitudes. An expanding Hadley cell means many common storm tracks are slipping towards the poles, taking their high winds – and associated rainfall – away from the temperate regions.

Roderick takes a more telescopic view: air movements are powered by differences in temperature at different places. The bigger the difference between warm and cold air, the stronger the wind. One effect of global warming is to flatten those differences. The poles are warming faster than the equator, winters are warming faster than summers, and nights warming faster than days. “Everything becomes more uniform,” Roderick says.

What does the drop in wind speed mean? The decrease in evaporation has immediate implications for the precision calculations used in modern irrigation, and more complex effects on rainfall patterns.

While less evaporation may be good for some plants in arid areas, stilling may make others less able to disperse wind-blown seed to suitable new habitats, and hence less resilient to climate change.

Less wind could also hurt city-dwellers. In what may be a taste of things to come, the winter of 2016/17 saw Europe becalmed, leading to smog so bad that Paris banned cars for six days, and the city of Skala in Poland briefly overtook Beijing atop the world’s air-pollution tables.

Potential effects on wind power are another area of concern, though there does not appear to be anything to worry about in the short term. Stilling has so far been detected only at heights up to 10 metres, while turbines harvest their energy 50 to 150 metres above the ground.

“We certainly haven’t seen anything that looks like stilling,” says Keith Ayotte, the chief scientist of Australian wind power outfit WindLab, who monitors more than 100 sites across the world where the company has turbines.

Though these higher-altitude winds will change over the 21st century, Vautard has used climate simulations to project the effect on total wind power available across Europe is unlikely to be more than 5%. One difficulty with prediction is a lack of observations. As McVicar notes, accurate and consistent measurements only exist “for the past 40 or 50 years”.

Cesar Azorin-Molina, a climate scientist at the University of Gothenburg in Sweden, has embarked on an EU-funded archival project with the effortful acronym STILLING: “TowardS improved undersTandIng of the worLdwide decline of wind speed in a cLImate chaNGe scenario.”

His mission is “rescuing historical wind speed data” like logbooks from Ponta Delgada in the Azores and Blue Hill Observatory in the US that go back more than a century. The age of anemometers – the devices that measure wind speed – can affect readings but, by compiling a single set of quality-controlled data, Azorin-Molina hopes to determine whether stilling is purely a recent phenomenon or if similar declines have happened in the past.

For McVicar, the stilling of the planet’s winds is a reminder that global warming has multiple and unpredictable flow-on effects. “We’re dealing with climate change, not just rising temperatures.”

Original Link

Eavesdropping on a twister

Each spring hundreds of tornadoes rip across the American heartland — so many that a belt from Texas to southern Canada is often referred to as Tornado Alley.

Scientists know surprisingly little about these small but deadly storms, whose wind speeds can exceed 320 kilometres per hour. Much of what they do know comes from a mix of Doppler radar and storm chasers who, in vehicles fitted out like mobile weather stations, pursue them overland, trying to get close-up measurements while remaining safely out of the storm’s path.

But this isn’t the only way tornadoes can be monitored. They also produce infrasound, says Brian Elbing, an experimental fluid mechanics researcher at Oklahoma State University, Stillwater, Oklahoma.

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Not to be confused with ultrasound (sound pitched above the limits of human hearing), infrasound is a low rumble at frequencies below the limits of human hearing. It came to prominence when scientists realized that it travels so far in the atmosphere that could be used to monitor nuclear bomb tests from half a globe away. More recently, scientists have realized that it is also produced by a wide array of natural events, ranging from earthquakes to meteors breaking up in the upper atmosphere.

One of these is tornadoes. Nobody is quite sure why they produce ultrasound, Elbing says, though his favorite theory is that it comes from oscillations in the radius of the tornado vortex. The frequency of these oscillations, he says, appears to be correlate to the size of the funnel cloud, which in turn is related to its destructive power.

In a paper presented at a meeting of the Acoustical Society of America, in Minneapolis, Minnesota, Elbing eavesdropped on an 11 May 2017 tornado and estimated, based on its ultrasound frequency, that it had a diameter of 46 meters. Later, he says, the official report from the US National Oceanic and Atmospheric Administration also put the diameter at 46 meters—a figure so close to his own group’s calculation that he jokes his group should have inserted some kind of error into their figures just to ensure people would believe them.

Despite his finding’s unexpected precision, Elbing notes that it’s still a pilot study. “We really need a lot more observations,” he says. Right now, he says, the scientific literature shows only a handful of detailed infrasound observations of tornadoes. “I’d say the number is less than ten.”

That said, he thinks that infrasound holds tremendous promise for tornado detection and monitoring. To begin with, tornadoes can show up on infrasound earlier than they do on Doppler radar. “We started detecting this one ten minutes before,” he says, adding that other studies have suggested that they might show up as much as an hour earlier.

Infrasound also works at longer ranges than radar because infrasound wraps around the curvature of the Earth, while radar travels in a straight line. That’s a big enough effect that tornadoes don’t have to be all that far way to hide from Doppler radar. Also the infrasound may be better at detecting storm systems with multiple tornadoes. In the case of his 11 May measurements, Elbing says, conventional measurements showed the presence of only a single tornado, while his data revealed two.

That said, Elbing may face an uphill battle in convincing other tornado researchers that he really has invented a better mousetrap. One of the sceptics is Howard Bluestein, a storm chaser and research meteorologist from the University of Oklahoma, Norman.

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“We currently rely on Doppler radar,” he says. “[Elbing] has presented evidence that there may be a sonic signal. If this is true, he would have to show why it is better than Doppler radar.”

Elbing counters that conventional tornado warnings aren’t actually all that accurate. Seventy-five percent, he says, turn out to be false alarms. Reducing that percentage is an obvious step toward getting people to take them more seriously.

Furthermore, he says, the greatest benefits of infrasound detection and tracking might not be in the prairie regions of Tornado Alley. “Oklahoma is a big, flat state,” he says. “Storm systems move in a line, so we predict them quite well.”

Of greater concern, he says, is a region he calls Dixie Alley, which encompasses much of the American South. Tornadoes here tend to be smaller than those on the Great Plains, he says, but they are also deadlier. One problem is mountainous terrain, which blocks Doppler radar signals. Another is a maze of twisty roads in which it’s easy to be trapped by an approaching storm. “Storm chasers will not go there,” Elbing says.

Original Link

Your next holiday might cost the Earth

Holidays are for relaxing, adventuring, or pampering yourself. But they can also be large contributors to global climate change. In fact, says Arunima Malik, a researcher in sustainability assessment at the University of Sydney in Australia, tourism accounts for a startling 8% of the world’s annual greenhouse gas emissions.

Furthermore, she and colleagues report in a paper published in the journal Nature Climate Change, these emissions increased 15% between 2009 and 2013, and could increase by another 45% by 2025, driven by increasing global affluence and the related rise in demand for energy-intensive travel.

Malik’s team wasn’t the first to address this problem. But prior studies, she says, had found tourism’s impact to be much lower — roughly 3% of the total.

The difference is because previous analyses looked primarily at the relatively direct greenhouse-gas impacts of tourists’ activities, she says, examining only the more obvious parts of the supply chains related to them. By combining several mammoth databases, she explains, her team was able to trace supply chains in far greater detail, for 160 individual countries.

“We were able to trace over a billion supply chains,” she says.

As a result, her team was able to account for such things as the construction materials for hotels and souvenir shops, the effects of tourism-related land-use changes, and all of the inputs that go into foods and beverages consumed by tourists.

“People eat more processed food when they travel,” she says.

Much of the impact is from carbon dioxide, but that isn’t the only greenhouse gas produced by tourism-related activities. One-sixth of the overall impact comes from methane, she says, mostly from agricultural activities designed to feed tourists. Nitrous oxide, chlorofluorocarbons, sulfur hexafluoride, and a couple of other gases also play a role.

But that was only part of the study. Malik’s team also calculated the carbon costs of tourism country-by-country, not just for destination countries, but for those from which tourists come.

Not surprisingly, tourists from high-income countries spent the most on air travel, hospitality, and shopping, racking up correspondingly high greenhouse gas footprints in return. Those from lower-income countries took more budget-minded vacations, eating fewer highly processed foods and doing a higher fraction of their travel by rail or automobile.

Among other things, the results revealed that a disproportionate fraction of emissions occurred on small island nations, which have relatively few ways to mitigate their climate-change footprints.

“This leaves them in a difficult situation because this is their income stream,” Malik says, adding that, at the same time, they have a lot to lose from unchecked emissions.

“They are really vulnerable to the effect of climate change,” she says.

Other scientists are impressed, but cautious. Paul Peeters, a professor of sustainable transport and tourism at Breda University of Applied Sciences in the Netherlands, applauds the new study’s focus on such factors as agricultural emissions.

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“The message that food should not be ignored is welcome,” he says. “Also the finding that emissions grow faster than economies in tourism is important.”

However, he says, the inclusion of so many other factors into the total has the unwelcome side-effect of masking the importance of air travel: a concern because the technology exists to significantly reduce the greenhouse-gas footprint of such things as agriculture, surface transport, heating, and construction.

“This is not the case for aviation,” he says. And that’s a problem, because the average distance that tourists travel is increasing rapidly.

“Aviation forms a fundamental threat to the success of the Paris Accord,” he says.

Another problem is that people eat and shop not just when they travel, but also at home. To the extent they are going to do these things regardless of where they are, they are not costs of travel, per se.

That said, the effect of the splurge-when-traveling effect appears to be huge, at least for tourists from wealthy countries. Peeters’ own work has found that the average Dutch tourist creates seven to eight times more carbon emissions on holiday than at home.

Malik agrees that her team’s study wasn’t able to take this into account. The goal, she says, was to tabulate all of the costs of tourism, in an effort to raise awareness of the degree to which it affects climate change.

“The more we talk about it, the more, hopefully, we’ll be able to find solutions for ensuring that tourism-related carbon emissions don’t keep on growing,” she says.

One such solution, says Richard Alley, a climate researcher at Pennsylvania State University in the US, is a “price” on greenhouse gas emissions, possibly as a carbon tax, or possibly via other methods such as cap-and-trade.

People pay for fossil fuels and things derived from them in order “to get good things from the energy,” he says. But in the process, greenhouse gas emissions from that energy produce damages, such as climate change. Economic studies, he explains, “repeatedly find that a price on carbon would allow people to continue to do the things they want, while balancing the good against the bad. This ‘right-pricing’ of carbon would help develop the technologies that will allow future travel and other activities we enjoy without changing the climate.”

Malik’s colleague, Manfred Lenzen, also of the University of Sydney, urges eco-minded tourists not to wait for the government to put such “right-pricing” into effect. Instead, he encourages them to take matters into their own hands and voluntarily invest in projects designed to offset their carbon emissions – especially from flying.

For example, he says, an air traveler could help fund a project designed to grow trees where none currently exist. But it isn’t cheap. “If I flew from Melbourne to the UK return, I would pay at least an additional $205 to offset my emissions,” he says. “For a return trip between Sydney and Brisbane, about $18 extra.”

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Dwindling desert dust spells danger for the Amazon

Global warming may cut the amount of dust blown into the atmosphere from the Sahara Desert by up to 100 million tonnes a year, starving the Amazon rainforest of nutrients and turning up the heat in the north Atlantic.

Rising temperatures will mean less wind and hence less dust, according to a paper posted on the arXiv preprint server by NASA earth scientist Tianle Yuan and colleagues. Previous attempts to predict future dust levels have had limited success, but the new paper argues they have ignored the key factor: the temperature difference between the north and south Atlantic.

Airborne dust is a surprisingly large player in the planet’s climate system: it both absorbs and scatters radiation from the sun, serves to seed clouds by providing nuclei for water droplets to grow around, and – when it finally falls back to the surface – can provide key minerals such as iron and phosphorus for plants and marine life. The amount of dust in the atmosphere in turn depends on climatic conditions such as temperature, rainfall, and wind speeds.

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The vast Sahara Desert of north Africa and the semi-arid Sahel region on its southern border are major sources of atmospheric dust. In an average year they contribute more than 180 million tonnes. Most of the dust is carried west over the Atlantic by the trade winds, and much of it falls into the sea, where it provides vital iron for phytoplankton to grow.

Around 27 million tonnes blows all the way to the Amazon basin in South America, delivering phosphorus that contributes to the riotous lushness of the rainforest.

As the world warms, climate scientists expect that the northern part of the Atlantic ocean will get hotter faster than the southern part. Southern hemisphere winds will rush northward to balance out the temperature contrast, meaning that the area where air circulation from the two hemispheres meets – a blustery band of latitude known as the intertropical convergence zone, or ITCZ – will drift northward.

This all adds up to weaker winds over the Sahara, resulting in less dust in the air. Depending on future carbon dioxide emissions, Yuan’s team calculate that the amount of dust could drop by as much as 60% by the end of the twenty-first century.

The authors checked their model against historical records and palaeoclimatic evidence, and found that temperature differences between the north and south Atlantic are correlated with levels of African dust over the last 17,000 years. They also found a decreasing trend in the amount of dust since 1980.

The decline in dust levels may become a self-reinforcing cycle. Another effect of the airborne dust is to provide shade that cools the north Atlantic. As the dust dwindles, clearer air will mean warmer seas – which in turn means less dust.

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Funding boost for reef science

Funding to the tune of $100 million for scientific innovation and research is a key part of a $6.4 billion project to help protect the Great Barrier Reef (GBR), announced by the Australian Government. The project is called Reef 2050 Long Term Sustainability Plan.

The GBR brings in many billions in tourism revenue, and sustains thousands of jobs. But it has been adversely affected by rising ocean temperatures and acidity, recurrent bleaching, and the crown-of-thorns starfish.

To combat these issues and more, the sizeable government investment will look to focus specifically on science and technology, in partnership with the Great Barrier Reef Foundation.

Premier agencies including the Australian Institute of Marine Science and Australia’s national scientific body, the CSIRO, will receive funds to work together to determine the best research and development program for reef restoration and how to obtain additional private funding.

The investment will also go towards supporting women and girls in the STEM fields, which could potentially lend a hand in future conservation efforts.

CSIRO CEO Larry Marshall and Australia’s Chief Scientist Alan Finkel will play key roles in advising the government ministers in charge of this ambitious undertaking.

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Early springs mean less food for hungry nestlings

For millennia, the oak forests of Britain have had a tightly timed spring-summer cycle – the oak leaves unfurl, the caterpillars feast on them, and the forest birds feed the caterpillars to their chicks. Now, with a warming climate, the leaves and caterpillars are emerging earlier, creating a mismatch between peak food resources and hungry chicks.

New research published in the journal Nature Ecology and Evolution suggests that as spring warming continues due to climate change, the hatching of forest birds will be “increasingly mismatched” with optimal caterpillar numbers.

“Forests have a short peak in caterpillar abundance, and some forest birds time their breeding so this coincides with the time when their chicks are hungriest,” says lead author Malcolm Burgess, of the University of Exeter and the Royal Society for the Protection of Birds (RSPB).

“With spring coming earlier due to climate change, leaves and caterpillars emerge earlier and birds need to breed earlier to avoid being mismatched. We found that the earlier the spring, the less able birds are to do this.”

Burgess and colleagues used citizen scientists to gather data on the oak-caterpillar-bird system across Britain, including the spring emergence of leaves, the amount of caterpillar droppings, known as frass, under the trees, and finally the timing of nesting of three forest bird species; blue tits, great tits and pied flycatchers.

Bird life cycles were calculated using first egg dates (FED) from across the region covering the period 1960 to 2016, using nests from 36,839 blue tits (Cyanistes caeruleus), 24,427 great tits (Parus major) and 23,813 pied flycatchers (Ficedula hypoleuca).

The researchers found substantial trophic mismatch in the oak forests across the United Kingdom.

The researchers found that in recent times maximum demand from nestlings and peak caterpillar numbers were out of synch on average by 3.39 days in blue tits, 2.01 days in great tits and a substantial 12.87 days for the pied flycatcher.

Burgess suggests that the greater mismatch in the pied flycatchers was due to the fact that “as migratory birds, they are not in the UK in winter and therefore are much less able to respond to earlier spring weather.”

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The mismatch between caterpillar abundance and great tit nestlings has been determined previously. However, this study presents the first assessment of whether the effect is greater in southern Britain than in the north. Surprisingly, early spring had the same effect in both regions.

Co-author Ally Phillimore, from the University of Edinburgh in Scotland, says, “We found no evidence of north-south variation in caterpillar-bird mismatch for any of the bird species. Therefore, population declines of insectivorous birds in southern Britain do not appear to be caused by greater mismatch in the south than the north.”

Oaks and winter moths (the main caterpillar food of the birds) have more plasticity than vertebrates in the timing of their spring cycles – and respond rapidly to warming temperatures.

It seems the only way the birds will catch up is to evolve.

“Our work suggests that as springs warm in the future, less food is likely to be available for the chicks of insectivorous woodland birds unless evolution changes their timing of breeding,” says another of the researchers, Karl Evans, from the University of Sheffield’s Department of Animal and Plant Sciences.

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California screaming: the biggest economy in the US faces catastrophic climate challenges

California, the most populous state in the US, faces a future marked by “precipitation whiplash events” – extreme swings between drought and floods – caused by human-induced climate change, according to a team of scientists from the University of California at Los Angeles.

They warn of flooding that “would probably lead to considerable loss of life and economic damages approaching a trillion dollars”.

Their report, published in the journal Nature Climate Change, says California’s rapid shift from severe drought between 2012 and 2016 to heavy rains and widespread flooding during the 2016-17 winter offers a compelling example of one such transition in a highly populated, economically critical and biodiverse region.

It takes on global significance when considering that California, with a population of 39.5 million people in 2017, has the largest economy in the US – the sixth largest in the world – and has accounted for about 20% of the nation’s economic growth since 2010.

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The state, covering more than 1000 kilometres north to south, has abundant water resources in the north and a complex network of infrastructure to bring it to the massive population centres in the south. The civil engineering and risk management practices that are in place have been predicated on a largely stationary climate, and most existing water storage and conveyance structures have been built under such assumptions.

The report notes that during the 2016-17 winter, hundreds of roads throughout California were damaged by floodwaters and mudslides, including an important bridge collapse, and that In February 2017 heavy runoff in the Feather River watershed contributed to the failure of the Oroville Dam’s primary spillway, culminating in a crisis that forced the emergency evacuation of nearly a quarter of a million people.

The report’s lead author, Daniel Swain, says the team used specific flood and drought events from California’s history as baselines for exploring the changing character of precipitation extremes. Taking data from the Community Earth System Model Large Ensemble (CESM-LENS) allowed them to directly quantify changes in large-magnitude extremes.

Swain says this approach gave his team a much larger sample size of data from which to draw inferences, “without making assumptions regarding the underlying precipitation distribution”.

“By selecting a wide range of wet, dry and dry-to-wet transition (that is, ‘whiplash’) events informed by historical analogues,” he explains, “we aim to provide a comprehensive perspective on the changing risks of regional hydroclimate extremes in a manner directly relevant to climate adaptation and infrastructure planning efforts.”

The researchers assessed simulated changes in the frequency of California’s precipitation extremes caused by increasing atmospheric greenhouse gas concentrations. Swain says they estimated how often these events occurred, based on direct observations or historical accounts.

They then deployed a simulated control model of pre-industrial events that occurred with comparable frequency and severity to those observed to get an idea of how often such events could occur, given the continued growth of greenhouse gas concentrations.

Their findings indicate both extreme dry seasons and whiplash events increased by more than 50% over much of the state, and extreme wet events increased by more than 100% over nearly the entire state.

Moreover, they report a substantial increase in the projected risk of extreme precipitation events exceeding any that have occurred over the past century, meaning that such events would be unprecedented in California’s modern era of extensive water infrastructure.

Taking as its benchmark California’s “Great Flood of 1862”, epic storms over just six days that caused widespread destruction across Southern California, the report says, “Few of the dams, levees and canals that currently protect millions living in California’s flood plains and facilitate the movement of water from Sierra Nevada watersheds to coastal cities have been tested by a deluge as severe as the extraordinary 1861-1862 storm sequence, a repeat of which would probably lead to considerable loss of life and economic damages approaching a trillion dollars.

“Our results suggest that such an event is more likely than not to occur at least once between 2018 and 2060, and that multiple occurrences are plausible by 2100 on a business-as-usual emissions trajectory.”

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How the 2016 bleaching altered the shape of the northern Great Barrier Reef

File 20180418 163978 1aql97h.jpg?ixlib=rb 1.1 Staghorn and tabular corals suffered mass die-offs, robbing many individual reefs of their characteristic shapes. ARC Centre of Excellence for Coral Reef Studies/ Mia Hoogenboom

In 2016 the Great Barrier Reef suffered unprecedented mass coral bleaching – part of a global bleaching event that dwarfed its predecessors in 1998 and 2002. This was followed by another mass bleaching the following year.

This was the first case of back-to-back mass bleaching events on the reef. The result was a 30% loss of corals in 2016, a further 20% loss in 2017, and big changes in community structure. New research published in Nature now reveals the damage that these losses caused to the wider ecosystem functioning of the Great Barrier Reef.

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Fast-growing staghorn and tabular corals suffered a rapid, catastrophic die-off, changing the three-dimensional character of many individual reefs. In areas subject to the most sustained high temperatures, some corals died without even bleaching – the first time that such rapid coral death has been documented on such a wide scale.

The research team, led by Terry Hughes of James Cook University, carried out extensive surveys during the two bleaching events, at a range of scales.

First, aerial surveys from planes generated thousands of videos of the reef. The data from these videos were then verified by teams of divers in the water using traditional survey methods.

Finally, teams of divers took samples of corals and investigated their physiology in the laboratory. This included counting the density of the microalgae that live within the coral cells and provide most of the energy for the corals.

The latest paper follows on from earlier research which documented the 81% of reefs that bleached in the northern sector of the Great Barrier Reef, 33% in the central section, and 1% in the southern sector, and compared this event with previous bleaching events. Another previous paper documented the reduction in time between bleaching events since the 1980s, down to the current interval of one every six years.

Different colour morphs of Acropora millepora, each exhibiting a bleaching response during mass coral bleaching event. ARC Centre of Excellence for Coral Reef StudiesStudies/ Gergely Torda

Although reef scientists have been predicting the increased frequency and severity of bleaching events for two decades, this paper has some surprising and alarming results. Bleaching events occur when the temperature rises above the average summer maximum for a sufficient period. We measure this accumulated heat stress in “degree heating weeks” (DHW) – the number of degrees above the average summer maximum, multiplied by the number of weeks. Generally, the higher the DHW, the higher the expected coral death.

The US National Oceanic and Atmospheric Administration has suggested that bleaching generally starts at 4 DHW, and death at around 8 DHW. Modelling of the expected results of future bleaching events has been based on these estimates, often with the expectation the thresholds will become higher over time as corals adapt to changing conditions.

In the 2016 event, however, bleaching began at 2 DHW and corals began dying at 3 DHW. Then, as the sustained high temperatures continued, coral death accelerated rapidly, reaching more than 50% mortality at only 4-5 DHW.

Many corals also died very rapidly, without appearing to bleach beforehand. This suggests that these corals essentially shut down due to the heat. This is the first record of such rapid death occurring at this scale.

This study shows clearly that the structure of coral communities in the northern sector of the reef has changed dramatically, with a predominant loss of branching corals. The post-bleaching reef has a higher proportion of massive growth forms which, with no gaps between branches, provide fewer places for fish and invertebrates to hide. This loss of hiding places is one of the reasons for the reduction of fish populations following severe bleaching events.

The International Union for Conservation of Nature (IUCN), which produces the Red List of threatened species, recently extended this concept to ecosystems that are threatened with collapse. This is difficult to implement, but this new research provides the initial and post-event data, leaves us with no doubt about the driver of the change, and suggests threshold levels of DHWs. These cover the requirements for such a listing.

Predictions of recovery times following these bleaching events are difficult as many corals that survived are weakened, so mortality continues. Replacement of lost corals through recruitment relies on healthy coral larvae arriving and finding suitable settlement substrate. Corals that have experienced these warm events are often slow to recover enough to reproduce normally so larvae may need to travel from distant healthy reefs.

Although this paper brings us devastating news of coral death at relatively low levels of heat stress, it is important to recognise that we still have plenty of good coral cover remaining on the Great Barrier Reef, particularly in the southern and central sectors. We can save this reef, but the time to act is now.

This is not just for the sake of our precious Great Barrier Reef, but for the people who live close to reefs around the world that are at risk from climate change. Millions rely on reefs for protection of their nations from oceanic swells, for food and for other ecosystem services.

The ConversationThis research leaves no doubt that we must reduce global emissions dramatically and swiftly if we are save these vital ecosystems. We also need to invest in looking after reefs at a local level to increase their chances of surviving the challenges of climate change. This means adequately funding improvements to water quality and protecting as many areas as possible.

Selina Ward, Senior Lecturer, School of Biological Sciences, The University of Queensland

This article was originally published on The Conversation and is republished with permission. Read the original article.

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Cropping, population boost carbon sinks

Research into the effect of wildfires on global warming has delivered a “good news/bad news/good news” result.

The first bit of good news, write scientists Vivek Arora and Joe Melton from government department Environment and Climate Change Canada, in the journal Nature Communications, is that the area burnt around the world by wildfires has been steadily decreasing since the 1930s. This also means that the amount of carbon dioxide released into the atmosphere by such fires has similarly dwindled.

The bad news, however, is that the result is due largely to the fact that there is, these days, much less wilderness to burn – the result of increasing farmland and human settlement.

But, Arora and Melton report, it’s not all bad news. The overall effect is to increase the amount of carbon being absorbed by the land – decreasing, thus, the amount directly contributing to global warming by accumulating in the atmosphere.

To make their findings, the researchers used sediment-charcoal records combined with satellite observations (in the latter case, from 1997 onwards) and fed the data into a complex Canadian-derived model that simulated additional inputs such as snow cover, soil temperature and soil moisture content.

The results showed that wildfires increased in number and extent from 1850 until the 1930s, at which point the effects of land clearing for both cropping and human settlement pushed the fire numbers downwards, a trend that has continued ever since.

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The reduction in fire outbreaks and area burnt does not directly correlate with the loss of wilderness. Instead, the effect is increased because of additional factors. These include the patchwork nature of cropland geographies, which inhibit the spread of active fires, and the use of deliberate fire-suppression technologies.

Many crop-farming strategies, of course, involve annual stubble burning, but Arora and Melton find that this contributes little to the total amount of fire-generated carbon produced, mainly because stubble comprises a far lower biomass than woodland or forest.

“Even when agricultural fires are considered together with wildfires, the overall effect of increase in cropland area at the global scale is to decrease area burned,” the pair write.

However, conversion of land to cropping alone does not lead to a decrease in carbon emissions, mainly because “the vegetation that is spared burning from wildfires was already deforested in the first place”. In addition, the trees that were cleared to create the fields goes through decomposition for several years afterwards, releasing carbon dioxide into the atmosphere.

However, when the whole model is considered – including cropland clearance, landscape fragmentation and fire suppression – the result is the creation of a significant carbon-sink reservoir.

On a global scale, of the total amount of anthropogenic carbon dioxide, some 45% stays in the atmosphere, while 30% enters the land and the remainder is sequestered in the oceans.

Using data covering the period 1960 to 2009, the researchers found that land clearance and increasing population density were responsible for an extra 130 million tonnes of carbon each year sinking into the land – about 19% of the total.

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Skating weather

This Copernicus Sentinel-2 image from 2 March 2018 shows Amsterdam and the IJmeer and Markemeer freshwater lakes covered by a thin layer of ice. A late winter cold snap was causing havoc throughout much of Europe, but the Dutch were busy dusting off their skates and eager to hit the ice.

The ice on these big lakes was much too thin to skate on, but some canals in Amsterdam were closed to boats to give the ice a chance to thicken and skaters took what is now a relatively rare opportunity to enjoy a national pastime.

In what may be evidence of a changing climate, the Netherlands doesn’t see the ice that it used to. The Royal Netherlands Meteorological Institute rates winters using an index: those scoring above 100 are considered cold. Between 1901 and 1980, there were seven winters above 200 – very cold. The last time the index exceeded the magical 100 mark was in 1997. In fact, this was also the last time the weather was cold enough for an ‘Elfstedentocht’: a 200 km skating race between 11 towns in the north of the country. In 2014, for the first time since measurements began, the index fell to zero.

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Mediterranean megaflood confirmed

Once upon a time there was a massive flood across the Mediterranean Sea, an in-pouring of water so huge that it excavated a canyon five kilometres deep and 20 kilometres long, and created a waterfall with a 1.5 kilometre drop.

Evidence for the great flood, long hypothesised, has now been found by a team of researchers led by geoscientist Aaron Micallef from the University of Malta.

And while several Mediterranean traditions feature great flood narratives, the earliest arising from Sumeria and already well enough known to be recorded in cuneiform by the seventeenth century BCE, this one is unlikely to have been the inspiration.

In a paper published in the journal Scientific Reports, Micallef and colleagues present geological evidence for an event known as the Zanclean megaflood, which took place around 5,300,000 years ago.

The flood was preceded by a catastrophic geologic transformation called the Messinian salinity crisis (MSC), described by the researchers as “the most abrupt, global-scale environmental change since the end of the Cretaceous”.

In the Mediterranean region, the crisis was caused by the closure of what today is known as the strait of Gibraltar, cutting the passage between the sea and the Atlantic Ocean. This occurred around six million years ago.

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As a result, there was a drastic imbalance created between evaporation rates and replenishing water intake. The Med transformed into two giant hypersaline lakes, separated by a land-bridge running from the toe of Italy, incorporating Sicily and ending at north Africa.

Sea levels are estimated to have dropped by between 1300 and 2400 metres. Salt deposits a kilometre thick settled on the sea floor.

Geographic evidence gathered in the 1970s led to the formation of the Zanclean megaflood hypothesis. Conclusive evidence, however, was lacking, leading some researchers to suggest the MSC was ended by a flow of brackish water from the Black Sea, with Atlantic inflow resuming only later.

In the latest research, using seafloor data from offshore eastern Sicily and the islands of Malta, Micallef’s team identifies a distinct body of sediment 160 kilometres long and 95 kilometres wide that lies on top of the saline deposits, ending abruptly against an undersea limestone cliff called the Malta Escarpment off eastern Sicily, and thinning down in a wedge-shape to the east.

The wedge is 900 metres deep in places. The researchers suggest it represents debris and sediment pushed eastwards by a surge of water coming in from the Atlantic upon the reopening of the Gibraltar strait.

The mass of water, carrying the debris, crested the land-bridge and plunged down the other side creating a five-kilometre-deep trench, still around today and known as the Noto canyon. It also careened down the Malta escarpment, dropping 1.5 kilometres.

Micallef and colleagues conclude that the evidence suggests the megaflood was a Mediterranean-wide event, rather than one restricted to its eastern reaches, as the Black Sea theory holds.

So powerful was the flood, it is estimated that the Med reversed water loses incurred over 640,000 years in just two.

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