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September 18, 2013 2:51 pm
The Arctic’s summer sea ice is set to nearly vanish in less than 40 years, according to the final draft of a sweeping UN climate change report that sharply revises past estimates of how fast the icy north is melting.
“A nearly ice-free Arctic Ocean in September before mid-century is likely,” says the draft seen by the Financial Times of the first large-scale study in six years by the Intergovernmental Panel on Climate Change.
The retreating ice is encouraging for Arctic nations such as Russia, which is trying to boost shipping traffic along its icy Northern Sea Route.
But it is worrying for scientists because of what was described in a recent study as an “economic time bomb” that could explode if the melting Arctic permafrost releases vast plumes of methane, a potent greenhouse gas, and drives significant climate change.
In its last report in 2007 the IPCC said the ice, which melts a little each summer then refreezes as winter nears, was expected to disappear “almost entirely by the latter part of the 21st century”. Both that projection and the revised one revealed yesterday depend on the rate of greenhouse gas emissions.
The new Arctic assessment is one of the more notable aspects of a report that more than 800 scientists from around the world have spent the last four years compiling on behalf of the nearly 200 governments that belong to the 25-year-old IPCC.
The first section of the mammoth study, which will be released in stages this year and next, is to be finalised in Stockholm next week. It examines the science of global warming and, like the rest of the report, is not based on original research but is an assessment of the fast-growing field of climate science.
The latest report is only the fifth of its type and the first since the IPCC admitted its 2007 report had wrongly suggested Himalayan glaciers could melt as early as 2035.
It is also the first to confront one of the more puzzling questions about climate change: why global temperature rises have slowed in the last 15 years even though atmospheric concentrations of carbon dioxide, the most important man-made greenhouse gas, have soared to record heights.
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The draft of the report’s 31-page summary for policy makers says there have been similar temperature slowdowns in the past, but the overall warming trend is clear, with global average combined land and ocean temperatures rising 0.89C from 1901 to 2012.
However, there is also a revised estimate of how much warming is likely to arise once carbon dioxide levels in the atmosphere double.
The last IPCC report suggested the lowest number was likely to be 2C while the one before said 1.5C. The latest one reverts to a figure of 1.5C but unlike the previous assessments it does not include a best estimate.
A central finding of the report, however, is that scientists are more certain than ever that humans are causing global warming mainly by pumping greenhouse gases into the atmosphere through the burning of fossil fuels such as coal and gas.
“It is extremely likely that human influence on climate caused more than half of the observed increase in global average surface temperature from 1951-2010,” the draft says.
“There is high confidence that this has warmed the ocean, melted snow and ice, raised global mean sea level and changed some climate extremes in the second half of the 20th century.”
Some aspects of the draft may change during next week’s meeting in Stockholm, but the central findings are not expected to be altered.
IPCC spokesman Jonathan Lynn said it could be misleading to draw conclusions from it at this stage.
“It will be finalised next week – the culmination of four years’ work by hundreds of experts who have volunteered their time and expertise – and we look forward to discussing its contents after that,” he said.
A nearly ice-free Arctic Ocean in September before mid-century is likely
- Leaked IPCC report, 2013
The new report also contains new projections of how fast global sea levels will rise because scientists have gained a better understanding of how the Greenland and Antarctic ice sheets are likely to influence such an increase.
This addresses one of the most heavily criticised aspects of the 2007 IPCC report, which did not give a complete estimate of how much sea levels would rise this century because of uncertainties about how the ice sheets were contributing to sea levels.
The question of when the Arctic’s summer sea ice will vanish has also been contentious.
Last year the summer sea ice shrank to its lowest level on record.
This summer, the ice has failed to decline at such a spectacular rate, which many sea ice experts had expected.
Some scientists, such as Professor Peter Wadhams of Cambridge university, predict it will vanish as soon as 2015.
Others say it is more likely to take decades rather than years.
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