Analysis

Antarctic ice shelf thinning is accelerating, reveals new study

  • 26 Mar 2015, 19:30
  • Robert McSweeney

Antarctic ice shelf | Shutterstock

A new study reveals ice shelves in the western part of Antarctica are melting much faster than a decade ago. Satellite data from three separate missions shows melting of these vast, floating ice shelves has increased by 70% in the last decade.

If current warming trends continue, the researchers say the ice could thin so much that these icy 'gatekeepers' risk collapsing, unlocking parts of the ice sheet to faster ice loss.

Floating sheets of ice

Ice shelves form where a glacier on land reaches the coast and flows into the ocean. They surround 75% of the Antarctic continent. If the ocean is cold enough, the ice doesn't melt but instead forms a floating sheet of ice that extends over the ocean.

Ice Shelf Diagram

Ice shelf diagram. Credit: Professor Helen Fricker, Scripps Institution of Oceanography, UC San Diego.

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Amazon rainforest is taking up a third less carbon than a decade ago

  • 18 Mar 2015, 18:05
  • Robert McSweeney

Amazon at dawn | P. van der Sleen

The amount of carbon that the Amazon rainforest is absorbing from the atmosphere and storing each year has fallen by around a third in the last decade, says a new 30-year study by almost 100 researchers.

This decline in the Amazon carbon sink amounts to one billion tonnes of carbon dioxide - equivalent to over twice the UK's annual emissions, the researchers say.

If this pattern exists in other forests around the world, deeper cuts in human-caused carbon dioxide emissions are needed to meet climate targets, the researchers say.

Three billion trees

The Amazon rainforest is the largest rainforest in the world. Spanning nine countries in South America, it's 25 times the size of the UK.

Using a process known as photosynthesis, the Amazon's three billion trees convert carbon dioxide, water and sunlight into the fuel they need to grow, locking up carbon in their trunks and branches.

As they grow, Amazon trees account for a quarter of the carbon dioxide absorbed by the land each year. Studies suggest that as human-caused carbon dioxide emissions increase, forests will absorb and store more carbon, assuming they have enough water and nutrients to grow.

But a new study, published today in Nature , suggests the Amazon has passed saturation point for how much extra carbon it can take up.

Diminishing carbon sink

A team of almost 500 people monitored trees in more than 300 sites across eight countries. Between 1983 and 2011, the researchers measured the trees in each plot, recording the number, size and density to calculate how much carbon each one stored.

The trees took up more carbon and grew more quickly during the 1990s, before levelling off since the year 2000. You can see this in the middle chart below.

Brienen Et Al (2015) Fig1

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Farming Africa’s wet savannahs would have a high climate cost, study warns

  • 17 Mar 2015, 14:10
  • Robert McSweeney

Irrigation in Zambia | Lyndon Estes

As the global population rises, some scientists have suggested that Africa's wet savannahs could be ideal for growing the extra crops needed to meet the growing demand for food and bioenergy.

But it isn't quite the solution it seems, according to new research. The idea that Africa can provide food and biofuels while keeping emissions low "does not add up", the researchers say.

The wet savannah

'Wet savannah' describes warm, tropical areas areas that are wet enough to support crops and aren't covered with dense forest. Africa is home to around half of the world's wet savannah. Much of it is found in the Guinea Savannah, which makes up around a third of sub-Saharan Africa

Searchinger Et Al (2015) Fig1

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La Niña boosts the odds of tornadoes and hailstorms in the US, study shows

  • 16 Mar 2015, 16:00
  • Robert McSweeney

Tornado on US plains | Shutterstock

Last week, scientists announced the arrival of a long-awaited El Niño event. It's well known that El Niño triggers extreme weather around the world. But a new study published today shows how the event's little sister, La Niña, can be destructive too.

La Niñas tend to bring more tornadoes and hailstorms to the southern US, the study finds. Knowing this will allow scientists to forecast hail and tornado frequency a season in advance for the first time, the lead author tells Carbon Brief.

El Niño and La Niña

Every five years or so, weakening trade winds cause a shift to warmer than normal ocean temperatures in the eastern equatorial Pacific Ocean. The phenomenon, known as El Niño, has a cold water counterpart, called La Niña. During La Niña, the opposite happens. The trade winds strengthen and the central and eastern Pacific Ocean become colder than normal.

Together, these warm and cold events form the El Niño-Southern Oscillation (ENSO), and cause most of the fluctuations in global weather we see from one year to the next.

The impact of ENSO events can be dramatic. La Niñas, for example, are known to bring floods to Central and South America, and hurricanes to the Atlantic Ocean.

Now a new paper, published in Nature Geoscience, suggests there could be a link with a different type of extreme weather event. The southern US is on the receiving end of more tornadoes and hailstorms during La Niña events and fewer during El Niños, the research finds.

La -nina

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Scientists link Arctic warming to intense summer heatwaves in the northern hemisphere

  • 12 Mar 2015, 18:00
  • Roz Pidcock

The Arctic is warming up, and the impacts are being felt right across the world. A new study suggests rising temperatures there could even be contributing to longer-lasting heatwaves in the northern hemisphere, like the one Russia experienced in 2010.

Published today in the journal Science, the paper is the latest in a line of research suggesting how rising temperatures in the high north could be affecting our weather patterns much further south.

But there's a lot still to understand before the links can be well and truly pinned down, scientists say.

Extreme Arctic warming

The Arctic is warming at least twice as fast as the globe as a whole. Scientists begun noticing the pattern emerge in temperature records since about the year 2000. It's known as  Arctic Amplification.

Part of the reason for it is that, as sea ice is diminishing, heat from the sun that would have been reflected back to space by snow and ice is being absorbed by the oceans instead, warming them up.

As the Arctic warms faster than the rest of the world, the temperature difference between the pole and the equator is getting smaller. Since this temperature contrast drives much of the atmospheric circulation in the northern hemisphere, the smaller it gets, the weaker the circulation becomes.

These atmospheric circulation patterns are responsible for delivering the weather systems that create warm, cold or wet conditions in the northern hemisphere. So, it follows that disrupting the circulation will, in turn, have consequences for the weather we see.

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Earth entering new era of rapid temperature change, study warns

  • 09 Mar 2015, 16:00
  • Robert McSweeney

Trees at sunset | Shutterstock

The rate of climate change we're experiencing now is faster than at any time in the last millennium, a new study shows.

Researchers compared how temperature varied over 40-year periods in the past, present and future, and concluded that the Earth is entering a new "regime" of rapid temperature change.

We're already locked into fast-paced changes in the near future because of past emissions, the researchers say.

That means we'll need to adapt to minimise the impacts of climate change, even if greenhouse gas emissions are cut substantially.

Peaks and troughs

A look back at how global temperatures have changed over the past century shows how temperature  rise of the Earth's surface has been anything but smooth.

These peaks and troughs are in part caused by natural phenomena, such as  volcanic eruptions and  El Niño, which influence the Earth's climate from year to year.

The graph below shows average global surface temperatures for every year back to the 1850s. You can see that temperature changes from decade to decade do not always happen at the same pace. This is the impact of  natural cycles in climate, which can either work to enhance or dampen the long-term warming trend over short timescales.

A new study, published in Nature Climate Change, shows how much faster temperature has increased in recent decades compared to any time over the last 1,000 years.

 

Tempdatasets 2--5_cropped

How the major global surface temperature datasets compare. Showing NASA GisTEMP (purple), JMA (orange), NOAA MLOST (green) and Met Office/CRU (blue). Credit: Rosamund Pearce, Carbon Brief

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Leaf-eating insects may limit how much carbon forests absorb, study says

  • 03 Mar 2015, 17:20
  • Robert McSweeney

Forest tent caterpillar | Mary Jamieson

Insects could restrict how well trees absorb and store carbon in the future, according to a new study. In experiments simulating carbon dioxide levels in 2050, insects munched their way through almost double the number of leaves than under current conditions.

With fewer leaves, the trees are likely to become less effective at absorbing carbon dioxide from the air, the researchers say.

Carbon dioxide fertilisation

Trees are the biggest carbon sink on land. Through a process known as photosynthesis, trees convert carbon dioxide, water and sunlight into the fuel they need to grow, locking up carbon in their trunks and branches as living biomass.

Research suggests that when there's more carbon dioxide in the air, trees grow more quickly because the rate of photosynthesis speeds up. This is called 'carbon dioxide fertilisation'.

Scientists expect that as human-caused carbon dioxide emissions increase, forests will absorb and store more carbon, assuming they have enough water and nutrients to grow.

But the results of a three-year experiment, just published in Nature Plants, suggests that insects, such as caterpillars, may make it harder for trees to absorb this extra carbon by munching their way through the trees' leaves. With fewer leaves to absorb sunlight, the trees can't photosynthesise as much, and they absorb less carbon dioxide from the air.

'Double whammy'

The researchers set up their experiment at the Aspen FACE facility (Free-Air Carbon Dioxide Enrichment) in Wisconsin in the northern US. At the facility, birch and aspen trees are surrounded by vertical vents that release different gases to simulate future conditions.

FACE Aerial 2005 -25

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Scientists discuss the role of climate change in the Syrian civil war

  • 02 Mar 2015, 20:00
  • Robert McSweeney

Aleppo, Syria in 2013 | Shutterstock

This month will see the civil war in Syria reach an inauspicious fourth birthday. Since the uprising in 2011, over 220,000 people have been killed and almost half the Syrian population have fled their homes.

Evidence suggests the conflict was triggered by a complex mix of social, political, economic and environmental factors. But new research finds that human-caused climate change could also have had an influence.

The study, published in the Proceedings of the National Academy of Sciences, suggests a severe drought that began in 2006 was a catalyst for the conflict, and that climate change has made such droughts in the region more than twice as likely.

Syrian conflict

On 15th March 2011, Syrian security services opened fire on pro-democracy protesters in the southern city of Dara'a, killing several people. The unrest that followed spread throughout the country over the ensuing months, and by February 2012, Syria had descended into civil war.

A study published last year found that a multi-year drought contributed to food shortages, urban migration, and unemployment in the run up to the conflict.

Now the new study says the drought had a catalytic effect on the unrest in Syria, and human-caused climate change has made the chances of such a severe drought between two and three times more likely.

Prof Richard Seager, a climate scientist at Columbia University and co-author on the new study, explains:

"We're not saying drought caused the war. We're saying that added to all the other stressors, it helped kick things over the threshold into open conflict. And a drought of that severity was made much more likely by the ongoing human-driven drying of that region."

Multi-year drought

Syria sits in a band of relatively moist and productive land in the Middle East, known as the Fertile Crescent. But between 2006 and 2010, the region was hit by the worst multiyear drought since 1940.

Syria gets almost all of its rain during its six-month winter, from November to April. In 2007-08, winter rainfall across Syria fell by a third, with some areas receiving no rain at all. The winter was the driest in the observed record, the researchers say.

The decreasing rainfall (shown in the top graph below) combined with rising temperatures (second graph) resulted in a decline in soil moisture (third graph), the researchers say. This had dramatic consequences for Syrian agriculture.

Kelley Et Al (2015) Syria Fig1

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New study directly measures greenhouse effect at Earth’s surface

  • 25 Feb 2015, 18:00
  • Robert McSweeney

Cloudy skies | Shutterstock

Scientists know that greenhouse gases in the atmosphere cause the Earth to warm. But measuring exactly how much heat they trap is harder than you might think.

Previous studies using satellites have established that more heat is entering the atmosphere than leaving it. But a new study goes a step further and directly measures the amount of warming greenhouse gases are producing at Earth's surface.

The paper provides the critical link between rising carbon dioxide concentrations and the extra energy trapped in the climate system, the researchers say.

Greenhouse effect

Joseph Fourier first suggested in the 1820s that gases in the Earth's atmosphere trap heat and help keep the planet warm, coining the term greenhouse effect. Physicist John Tyndall later extended the theory by identifying the gases, such as carbon dioxide and methane, that were responsible for the warming.

Jumping forward a century and a half, we now know a lot more. Using satellites to measure how much of the sun's energy enters the Earth's atmosphere, and how much is reflected or re-emitted back into space, scientists have shown that the difference between the two is increasing. This means the Earth is trapping more heat than it used to, and therefore must be warming.

But while those studies show a widening gap between the energy reaching and leaving Earth, they are unable to directly measure how much warming greenhouse gases are causing at a particular point in time. New research, published today in Nature, shows how scientists have directly been able to measure the warming effect of greenhouse gases at Earth's surface.

Measuring energy

The researchers used a set of instruments to take thousands of measurements at the Earth's surface. The instruments record the longwave energy that is re-emitted by greenhouse gases back towards the Earth's surface, which causes the warming.

Making these sorts of measurements on the ground is difficult, says lead author Dr Daniel Feldman, a geological scientist at the Lawrence Berkeley National Laboratory in the US. With weather systems passing overhead, and temperatures and humidity changing frequently, it's tricky to take energy measurements without other factors getting in the way.

To overcome this problem, the researchers measured temperature and water vapour at the same locations so that their influence on warming could be eliminated from the calculations, leaving just the impact of greenhouse gases.

The scientists used data from 2000 to 2010, collected from two sites in the US: the southern Great Plains and northern Alaska. They chose these sites because of their very different climates, says Feldman. This meant the researchers could investigate both a mid-latitude and a high-latitude location.

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Surface warming 'hiatus' could stick around another five years, say scientists

  • 23 Feb 2015, 16:30
  • Roz Pidcock

Don't be surprised if the slower pace of warming we're seeing at the Earth's surface lasts for another five years, scientists say.

new paper out today puts the chances of the so-called "hiatus" staying until the end of the decade at about 15 per cent, or one in six.

But the heat hasn't gone away. The scientists say most of it is lurking in the deep ocean and we can expect the pace of warming to pick up when this heat gets released again.

Slower surface warming

Since 2000, the temperature at the Earth's surface  hasn't warmed as quickly as it has in previous decades, despite greenhouse gas emissions rising  faster than they were before.

A growing body of evidence is  homing in on the  Pacific Ocean as the main culprit for why we're seeing "unexpectedly modest" warming, as the Nature Climate Change paper puts it.

Scientists think a natural fluctuation is causing heat to find its way to the deep ocean in the Pacific, where it doesn't warm the atmosphere as much it would if it stayed at the surface.

A number of recent studies have found that periods of faster and slower warming  aren't unusual in Earth's temperature record. It's what scientists expect as these natural cycles flip-flop between their  different phases, superimposed on top of greenhouse gas warming.

But what are the chances of natural variability being strong enough to offset some, or even all of the warming expected from greenhouse gases?

The new paper by Dr Chris Roberts, an ocean and climate specialist at the Met Office Hadley Centre, and colleagues at the University of Exeter sheds some new light on this question.

Odds of a 'hiatus'

The new paper uses a suite of climate models to examine past temperatures with and without greenhouse gas forcing. The authors find there's a 28 per cent chance natural variability could cause a five-year long 'hiatus'.

The scientists define 'hiatus' as a period during which the observed temperature rise is less than the warming expected from greenhouse gases of 0.2 degrees Celsius per decade.

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