Monash says tropical Pacific “sweet spot” partly responsible for Arctic warming

2 June 2014

An international team of scientists estimate that up to half of the recent global warming in Greenland is caused by natural climate variations.

Monash University Environmental Sciences
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The research, published recently in the journal Nature, sheds new light on the rapid melting of Greenland’s glaciers. Crucially it indicates that global warming caused by carbon dioxide emissions may not be the only factor responsible.
Dr Ailie Gallant from Monash University School of Geography and Environmental Science said these natural variations stem from an unusually warm tropical Pacific Ocean, east of Papua New Guinea. This “sweet spot” is partly responsible for Arctic warming.
“A lot of the time, major climate changes are attributed to global warming caused by carbon emissions. But we can’t forget that natural climate variations can also have a significant part to play,” Dr Gallant said.
“Carbon dioxide emissions remain the key cause of global warming. But if we can learn more about how and why natural climate variations occur, we can better understand what we might expect from future climate changes and put plans in place to minimise or potentially reduce impacts.”
The team focused on the Arctic region, which has warmed more rapidly than the Earth as a whole. Greenland and parts of eastern Canada have experienced some of the most extreme warming since 1979, at a rate of 1 degree Celsius per decade—twice the global average.
Examining atmospheric temperature and pressure data from 1979 to 2012, the scientists discovered evidence that natural climate variations are impacting on this area of the Arctic at the same time as human-induced climate change.
Professor David Battisti from the University of Washington said that the data indicates that roughly half of the recent warming in Greenland is due to natural climate variations; the other half is caused by carbon emissions from humans.
“Nothing we have found challenges the idea that globally, glaciers are retreating. We looked at this place because the warming there is really remarkable. Our findings help us to understand on a regional scale how much of what you see is human induced by the build up of CO2 and how much of it is natural variability,” Professor Battisti said.
Scientists have known about these natural variations for some time. Until now little was known about their role in climate change in this region.
The team used observations and used advanced computer models to reveal that a warmer western tropical Pacific Ocean has caused atmospheric changes over the North Atlantic, warming the surface by about half a degree per decade since 1979.
What remains unknown is whether the enhanced warming in Greenland will continue.
Professor John Wallace from the University of Washington said that if ocean surface temperatures in the Pacific changes, it could result in a reduction in the amount of warming in Greenland.
“Ice is exquisitely sensitive to temperature, more than we ever would have thought. Natural variations could either accelerate or decelerate the rate of melting of Greenland’s glaciers in coming decades, but in the long run, the human induced component is likely to prevail,” Professor Wallace said.

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