Melting moments you don't want. Photo: Andrew Bain
Ice in Antarctica and Greenland is disappearing faster and may drive sea levels higher than predicted this century, according to leaked United Nations documents.
Greenland's ice added six times more to sea levels in the decade through 2011 than in the prior 10 years, according to a draft of the UN's most comprehensive study on climate change. Antarctica had a fivefold increase, and the UN is raising its forecast for how much the two ice sheets will add to Earth's oceans by 2100.
The changes in the planet's coldest areas are a “very good indicator” of a warming planet, according to Walt Meier, a research scientist with the U.S. National Aeronautics and Space Administration.
“It's an early warning system,” Meier said in a phone interview from NASA's Goddard Space Flight Center in Greenbelt, Maryland. “When you think about a couple of degrees of warming, in the UK or US, it's not something that would be too noticeable, whereas in an area of snow and ice, it can have a huge effect. With sea ice, minus 1 to plus 1 is the difference between skating on the ice and swimming in the ocean.”
Greenland and Antarctica contain enough ice to raise global sea levels by almost 66 meters, a process that would take thousands of years.
The data is included in chapters of the study covering rising sea levels and the planet's cryosphere regions, the frigid realms of glaciers, permafrost, snow-covered ground and ice sheets. A draft of the 2,200-page study by the UN Intergovernmental Panel on Climate Change was obtained by Bloomberg from a person with official access to the documents who declined to be further identified because it hasn't been published.
A summary of the report designed to guide lawmakers worldwide as they work to devise climate policies that curb carbon emissions is due for publication on Sept. 27 in Stockholm, after a four-day meeting where the wording will be finalised. Jonathan Lynn, a spokesman for the panel, declined to comment.
Greenland's contribution to rising sea levels “very likely” rose to an average of 0.59 millimeters a year from 2002 to 2011, from 0.09 millimeters a year in the prior decade, according to the draft. The rate in Antarctica “likely” rose to 0.4 millimeters a year from 0.08 millimeters, it said.
The report defines “very likely” as a probability of greater than 90 per cent and “likely” is at least 66 per cent.
Greenland may add a total of 4 centimeters to 21 centimeters to ocean levels by the period 2081 through 2100, across a range of carbon-emissions scenarios assessed in the study, compared with the period 1986 through 2005. That's up from a 2007 forecast of 1 centimeter to 12 centimeters, when the UN carried out its last major assessment of climate science.
Results due to Antarctic ice range from lowering sea levels by 6 centimeters to a 14-centimeter increase. The 2007 report forecast a reduction of 2 centimeters to 14 centimeters, due to higher snowfall than surface melt. The UN said in the earlier report that its understanding of how the southern continent loses ice from glaciers flowing into the sea wasn't good enough to include in its prediction.
The authors of the latest report said there has been “substantial progress in ice-sheet modeling” since 2007. Even so, there remain “significant challenges” in modeling Antarctic glaciers and ice sheets that terminate at the sea, and the forecast for their contribution to sea levels by 2100 was the same across all different emissions scenarios examined, unlike with Greenland.
“We've had a major step forward in our ability to understand” ice patterns in Greenland and Antarctica, Martin Siegert, a glaciologist at the University of Bristol in England, said in a phone interview. “There is more certainty around the data.” Siegert wasn't involved in the IPCC report.
Other findings in the report include:
- Arctic sea ice extent “very likely” decreased 3.5 per cent to 4.1 per cent a decade since 1979, when satellite measurements began. Ice cover at the end of the annual melt season “very likely” decreased at a rate of 11.5 per cent a decade.
- The extent of Antarctica's sea ice “very likely” increased 1.2 per cent to 1.8 per cent a decade over the same period.
- “Almost all glaciers worldwide have continued to shrink” since the 2007 UN assessment. Their contribution to rising sea levels “very likely” averaged 0.62 millimeters a year from 1971 to 2009.
- More than 600 glaciers have reportedly disappeared “but the real number is certainly higher.”
- There's “very high confidence” that snow cover has decreased in the Northern Hemisphere since the 1920s.
- There's “high confidence” that permafrost temperatures have increased in “most regions” since the early 1980s.
“It's clear that the cryosphere is one of the natural indicators of decadal climate change in the planet,” David Vaughan, a researcher at the British Antarctic Survey in Cambridge, England, and a coordinating lead author of the UN report's chapter on ice, said in a phone interview. “The changes are very visible.” Vaughan declined to comment on specific findings of the report.