A Single Degree of Warming Is Key to Keeping Arctic Frozen

This is a polar bear still-hunting at a seal hole on the sea ice of the southern Beaufort Sea.
(Mike Lockhart, USGS)

(CN) – Scientists say limiting climate change-induced warming to just 1 degree Fahrenheit could prevent the Arctic from becoming ice-free in future summers.

A University of Colorado-Boulder study, published Monday in the journal Nature Climate Change, shows that limiting warming to 2.7 degrees Fahrenheit – the Paris Climate Agreement target – reduces the likelihood of an ice-free Arctic summer to 30 percent by the year 2100. In contrast, warming by 3.6 degrees Fahrenheit makes at least one ice-free summer a certainty.

The extent of Arctic sea ice has declined overall in recent years as global temperatures have spiked, but the effects of future warming remain uncertain. The new findings illustrate different scenarios of carbon dioxide emission levels lead to drastically different results for Arctic summer sea ice.

Alexandra Jahn, author of the study and an assistant professor in CU-Boulder’s Department of Atmospheric and Oceanic Sciences and a fellow in the Institute of Arctic and Alpine Research said the results came as a surprise.

“I didn’t expect to find that half a degree Celsius would make a big difference, but it really does,” Jahn said. “At 1.5 degrees Celsius, half of the time we stay within our current summer sea ice regime whereas if we reach 2 degrees of warming, the summer sea ice area will always be below what we have experienced in recent decades.”

The researchers used simulations from the Community Earth System Model run at the National Center for Atmospheric Research. They examined warming scenarios using the worldwide benchmark of 1.5 degrees Celsius of warming, set by the international Paris Climate Agreement in 2015, at the low end up to 4 degrees Celsius, or 7.2 degrees Fahrenheit, at the high end.

“This dataset allows us to predict how soon we’re likely to see ice-free conditions as well as how often,” Jahn said. “Under the 4-degree Celsius scenario, we would have a high probability of a three-month ice-free period in the summer months by 2050. By the end of century, that could jump to five months a year without ice. And even for half that warming, ice-free conditions of up to 2 month a year are possible by the late 21st century.”

The probability of ice-free summers drops by 70 percent if warming stays at 1.5 degrees Celsius. This could delay or possibly even stop an ice-free occurrence from happening, according to the researchers.

Jahn said the significant difference in the results might provide added incentive for countries to hit the 1.5-degree Celsius warming target in order to preserve current ecological conditions.

“The good news is that sea ice has quick response times and could theoretically recover if we brought down global temperatures at any point in the future,” according to Jahn. “In the meantime, though, other ecosystems could see permanent negative impacts from the ice loss, and those can’t necessarily bounce back.”

Several wildlife species, including polar bears and seals, rely on ice cover to survive. Humans in remote Arctic villages in turn depend on annual harvests of these ice-dependent species for year-round sustenance.

The study was jointly funded by CU-Boulder and the National Science Foundation.


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