The thaw could also trigger the release of millions of tonnes of greenhouse gases from once-frozen tundra, and disrupt Arctic Ocean currents and, by 2100, only the islands of the Arctic archipelago and Greenland will still harbour ground that remains frozen year-round nearly to the surface, says the study from two leading US climate modellers.
McGill University professor Nigel Roulet, a Canadian pioneer in permafrost research, called the study “provocative and scary” but also consistent with recent observations of actual thawing in Russia, Alaska and the Canadian Arctic. “This is not la-la land. We’re already seeing this but it’s good to have the numbers,” Roulet said in an interview. The McGill professor, who was not involved in the study, said the biggest impact for Canada would likely be on northern infrastructure, both that already built and major onstruction now on the drawing boards. “How can you design a pipeline down the Mackenzie to operate safely for 50 or 60 years when the very ground beneath is going to change substantially in that time,” he asked.
Permafrost occurs when the ground stays at a temperature of 0C or lower for a minimum of two years. Federal government surveys have found that permafrost underlies about half the land mass of Canada, extending as much as 700m deep in the Arctic archipelago. The top slice of ground in permafrost zones that freezes and thaws annually is called the ‘active layer’. In the high Arctic, no more than the top 300mm currently thaws, so footings and foundations for buildings and other structures are drilled lower to avoid damage from heaving. In places like Yellowknife the active layer can extend 1m deep.
But the new study projects that the active layer in Canada’s permafrost regions will at least triple in depth every summer to nearly 3.5m. The thawing might go deeper, but the computer model used for the study could simulate soil freezing and thawing only to that depth.
David Lawrence, chief author of the study, said how deep the permafrost thawing may extend is a crucial question to be tackled by further research. “The model projects large changes to this near-surface permafrost, but cannot say what will happen to the deeper permafrost, which is unlikely to be strongly affected by global warming,” Lawrence wrote in an email from the National Center for Atmospheric Research in Boulder, CO, where he is a climate scientist. Lawrence said he hopes to collaborate with Vladimir Romanovsky, a permafrost researcher at the University of Alaska Fairbanks, to fine-tune studies to deal with those deeper layers.
Romanovsky, who monitors permafrost observatories for the university’s Geophysical Institute, does not agree with Lawrence that the thaw could be so large, Associated Press reports. If air temperatures increase one to 2C over the next century, permafrost would begin thawing south of the Brooks Range and start degrading in some places on Alaska’s Arctic slope, Romanovsky said. However, a prediction that melting will reach deeply over the entire region goes too far. But Lawrence and co-author Andrew Slater concluded that only about one-tenth of the world’s 10.5m sqkm of continuous permafrost would emerge relatively-unscathed from global warming by the end of the century. The more-southerly areas where permafrost exists in patches “Ó called discontinuous or sporadic “Ó would certainly also thaw deeper from global warming, but these regions were not included in the computer projections.
The thawing forecast is based on a widely accepted scenario of atmospheric levels of carbon dioxide and other greenhouse gases continuing to rise from industrialization in China and India, combined with only modest controls like the Kyoto Protocol in developed countries. Even if nations cut greenhouse gas emissions in half by 2100, no more than 40% of today’s permafrost would still be frozen year-round in the uppermost layer, the study forecasts. The US researchers also warn that ground ice melting in the permafrost could help swell annual freshwater runoff to the Arctic Ocean by as much as 28% by the end of the century. This increase could trigger a domino effect that interferes with the vital heat-carrying currents in the Atlantic Ocean.
The permafrost study appears in the end-December issue of Geophysical Research Letters, published by the American Geophysical Union. Some results were also presented in November at an AGU conference in San Francisco.