thaws

Arctic sea ice has shrunk to near-historic lows during this Northern Hemisphere summer. The minimum extent for the year occurred on September 11th. Ice cover in the Arctic Ocean has been shrinking and thinning for more than 40 years. The amount of frozen seawater in the Arctic goes up and down during the year as sea ice thaws and regrows between seasons.

This year, the minimal extent of sea ice shrank to 1.65 million square miles. That’s about 750,000 square miles less than the average for late summer over the years between 1981 and 2010, representing a decrease of more than 30%. The all-time low of 1.31 million square miles was actually set in 2012. Sea ice coverage can fluctuate from year to year, but it has trended downward since it has started being tracked in the late 1970s. The loss of sea ice has averaged about 30,000 square miles per year.

Sea ice extent has not only been shrinking; the ice has been getting younger and thinner. Presently, the overwhelming majority of ice in the Arctic Ocean is first-year ice, which is thinner and less able to survive the warmer months. There is far less ice that is three years or older.

Meanwhile, sea ice in the southern polar regions was also low this year. In the sea around Antarctica, scientists are tracking near record-low sea ice at a time when it should have been growing extensively during the darkest and coldest months in the Southern Hemisphere.

Polar ice loss compounds polar ice loss. The loss of sea ice increases heat in the polar regions, where temperatures have risen about four times more than the global average.

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Arctic Sea Ice Near Historic Low; Antarctic Ice Continues Decline

Photo, posted September 15, 2016, courtesy of Mario Hoppmann via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Permafrost covers about a quarter of the landmass in the Northern Hemisphere. It stores vast quantities of organic carbon in the form of dead plant matter. As long as it stays frozen, it is no threat to the climate. But as it thaws, microorganisms start breaking down that plant matter and large amounts of carbon are released into the atmosphere in the form of carbon dioxide and methane.

This process has often been described as a ticking timebomb for the climate. The theory is that once global warming reaches a certain level, the process will become self-amplifying setting off a catastrophic amount of warming. If that level was reached, it would be a tipping point in the changing climate.

An international research team from the Alfred Wegener Institute in Germany has extensively researched this hypothesis. Their conclusion is that within the permafrost, there are multiple geological, hydrological, and physical processes that are self-amplifying and, in some cases, irreversible. However, these processes act only locally or regionally. There is no evidence that some particular threshold in global warming could affect all permafrost and accelerate its thawing on a global level.

This research does not mean that Arctic permafrost is nothing to worry about. In fact, there are ways in which it is more worrisome. Because the permafrost is very heterogenous – meaning it is very different in different places – there will be numerous small, local tipping points that will be exceeded at different times and at different levels of warming. All of this will proceed in step with global warming, contributing to the overall worsening situation. There is no warming level below which permafrost thawing is not a problem.

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Thawing permafrost: Not a climate tipping element, but nevertheless far-reaching impacts

Photo, posted January 24, 2014, courtesy of Brandt Meixell / USGS via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio