Climate science

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

  • 02 Mar 2015, 20:00
  • Robert McSweeney

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

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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