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Roz Pidcock

26.12.2014 | 10:25am
Temperature Ice Five bits of research that shaped climate science in 2014
TEMPERATURE|ICE| December 26. 2014.10:25
Five bits of research that shaped climate science in 2014
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Climate science never stops developing. Over the course of the year we’ve covered a myriad of scientific studies, some of which have made the news, and others which have been more quietly received. Here’s our pick of the papers that have shaped scientific discussion about climate change in 2014.

1. Pacific winds drive surface warming slowdown

In February,a paperby Matthew England and colleagues helped shed light on why surface temperatures have risenmore slowlyover the last 15 years or so than in previous decades, even though we’re emitting greenhouse gasesfaster than ever before

England et al (1).png

Colours show temperature trends in the Pacific during 1992-2011 at the sea surface. Trade winds blowing east to west are shown by the blue arrow. Thin arrows indicate a strengthening circulation, with more water transported to deeper layers. Source: England et al. (2014)

Afew pieces of researchlast year pointed towards thetropical Pacificas holding the key. The England paper added a layer of detail by describing the process that could be at play.

Trade winds have beenparticularly strongsince about 2000, which is driving heat deeper into the oceans and bringing cooler water up. This has made earth’s average surface temperature0.1 to 0.2 degreescooler than it would otherwise be, the scientists estimate.

While scientists suggest there could be anadditional rolefor the Atlantic in driving the hiatus,evidencefor the Pacific Ocean mechanism seems to bewinning outat the moment.

For more on how the ocean deeps influence what we feel up here on earth’s surface, here’s ourtop to bottom lookat the oceans and climate change.

England, M. et al. (2014) Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus. Nature.doi:10.1038/nclimate2106

2. West Antarctic glaciers show signs of collapsing

Scientists have long suspected the west Antarctic ice sheet is vulnerable to collapsing under rising temperatures – potentially raising global sea levels by several metres, eventually.

Apaperby Ian Joughin and colleagues in May suggested the chain of events leading to collapse may已经underway.It won’t be quick – probably taking several centuries. But beyond a certain point, the process is likely to be unstoppable, the scientists warned.

Aseparate paperby Eric Rignot described extensive satellite, air and ground surveys, which found not only are West Antarctic glaciers shrinking but there are no landscape features – like ridges, or other obstacles – stopping the ice from melting away completely.

Here’s NASA glaciologist Eric Rignot to explain.

So are the glaciers retreating or collapsing entirely? And do scientists think the collapse of the WAIS glaciers is “unstoppable”? We’ve answered some questions the research raised,here

Joughin, I., Smith, B. E. & Medley, B. (2014) Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West AntarcticaDOI: 10.1126/science.1249055

Rignot, E. et al. (2014) Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica, from 1992 to 2011. Geophysical Research Letters.DOI: 10.1002/2014GL060140

3. Antarctic sea ice measurements hit record high

This year, the amount of ice surrounding Antarctica reached arecord highof 22.11 million square kilometres. Antarctic sea ice extenthas grownat a rate of about1.5 per centper decade since 1979, according to satellite data.

Sea ice surrounding Antarctica reached a new record high extent in 2014.
On Sept. 19, 2014, the five-day average of Antarctic sea ice extent exceeded 20 million square kilometers for the first time since 1979. The red line shows the average maximum extent from 1979-2014. NASA’s Scientific Visualization Studio/Cindy Starr

Scientists know the Greenland and Antarcticice sheetsare losing ice, and thatArcticsea ice loss is accelerating. But pinning down why the opposite is happening in Antarctica is proving more difficult.

Scientists say changes in localwindpatterns and ocean circulation are the most likely candidates, delivering cold water to the surface which then freezes.

But apaperback in July by Ian Eisenmann and colleagues suggested there may be another explanation – a change in the way measurements are made, rather than in the sea ice itself.

In 2007, NASA updated its main sea ice dataset. Eisenmann found this had the effect of pushing sea ice values down a bit before 1991 and up a bit afterwards, which makes the growth in sea ice appear quite a lot bigger than before.

The authors say they can’t be sure yet if the old dataset is wrong, or the newer one, so it may well not be that significant. But if it’s the latter, that raises the possibility that Antarctic sea ice growth has been overestimated. You can read more about what other scientists had to say about the new paper,here

Eisenman, I. et al., (2014) A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated? The CryosphereDOI: 10.5194/tc-8-1-2014

4. The link between Arctic sea-ice loss and extreme winters got a bit stronger. Maybe

Temperatures in the Arctic are increasing almosttwice as fastas the global average – a phenomenon known as Arctic Amplification.

Apaperpublished in October by Masato Mori and colleagues was thelatest in a serieslinking rapidly increasing temperatures in the Arctic to very cold winters in the northern hemisphere.

CAPTION: Surface air temperatures over the Barents and Kara seas during winter, compared to the 1979-2013 average. Blue and red dots indicate severely cold and warm winters, respectively.

Jennifer Francis and Steve Vavrus first put forward the hypothesis that Arctic Amplification could affect northern hemisphere weather by influencing thejet stream– a band of fast-flowing air high up in the atmosphere.

While Francis told us she thinks therecent papermeans the mechanism is a“done deal”,not everyone is asconvinced.It’s a very new area of research and there is relatively little data to work with, as Arctic amplification only emerged as a strong signal in the mid-1990s.

The long-term picture suggests these cold winters might only be a temporary feature before further warming takes hold, Mori and colleagues suggest.

Mori, M. et al. (2014) Robust Arctic sea-ice influence on the frequent Eurasian cold winters in past decades, Nature Geoscience,doi:10.1038/ngeo2277

5. Record summer heatwaves are ten times more likely with climate change

Screen Shot 2014-12-08 At 15.08.47

European summer average temperatures with climate change (left) and without climate change (right). Red lines show actual temperatures relative to the long-term average. Christidis et al. (2014)

Climate change is raising the odds of summer heatwaves in Europe by a factor of 10, according toresearchfrom the Met Office. Over the past 10 to 15 years, the likelihood of a ‘very hot’ summer has risen – from once every 50 years to once every five years.

The summer of 2003 wasthe hottest ever recordedfor central and western Europe, with average temperatures in many countries as much as five degrees higher than usual.

To see how climate change is affecting the likelihood of heatwaves and other extreme events, researchers carry out single-eventattribution studies.第一个研究早在2004年就发现the 2003 heatwave was mademore than twice as likelybecause of climate change.

The new paper finds the rising impact of humans on the climate means the risk of ‘extremely hot’ summers is now ten times greater than when the 2003 European heatwave struck.

As the frequency of heatwaves increases, so do risks to human health. Building resilience to high temperatures is critical for limiting deaths during extended hot weather, the authors warn.

Christidis, N. et al. (2014) Dramatically increasing chance of extremely hot summers since the 2003 European heatwave, Nature Climate Change,http://dx.doi.org/10.1038/nclimate2468

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