Sea ice in the Arctic grew to its annual maximum level last week and joined 2015, 2016 and 2017 as the four lowest maximum extensions on record, according to scientists from the National Snow and Ice Data Center (NSIDC) and NASA. .
On March 17, the Arctic sea ice sheet peaked at 5.59 million square miles (14.48 million square kilometers), becoming the second-lowest maximum on record, at approximately 23,200 square miles (60,000 square kilometers). larger than the all-time high reached on March 7, 2017.
More significantly from a scientific perspective, the last four years reached nearly equal maximum extents and continued the decades-long trend of declining sea ice in the Arctic. The maximum extent this year was 448,000 square miles (1.16 million square kilometers), an area larger than Texas and California combined, below the average maximum extent from 1981 to 2010.
Each year, the sea ice sheet that covers the Arctic Ocean and surrounding seas thickens and expands during the fall and winter, reaching its maximum annual extent sometime between late February and early April. The ice thins and shrinks during spring and summer until it reaches its minimum annual extent in September. Arctic sea ice has been declining during both the growing and melting seasons in recent decades.
The decline of Arctic sea ice cover has myriad effects, from changes in climate and weather patterns to impacts on ice-dependent plants and animals, and the indigenous human communities that depend on them. The disappearance of ice is also altering shipping routes, increasing coastal erosion and affecting ocean circulation.
"The Arctic sea ice sheet continues to trend downward and this is related to the current warming of the Arctic," said Claire Parkinson, senior climate scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It is a two-way street: warming means that less ice will form and more ice will melt, but also, because there is less ice, less incident solar radiation is reflected, and this contributes to warming"
The Arctic has been through repeated hot spells this winter, with temperatures rising more than 40 degrees above average in some regions. The North Pole even experienced temperatures above freezing for a few days in February.
In mid-March, colder temperatures and winds pushed the edge of the sea ice sheet and caused a late increase in ice growth that brought the line closer in recent years.
In February, a large area of open water appeared on the sea ice sheet north of Greenland, within the multi-year ice pack - the oldest and thickest ice in the Arctic. Most of the opening has refrozen, but the new ice is expected to be thinner and more brittle, and a new opening could appear during the melting season. This could make the ice in this region more mobile and prone to leaving the Arctic this summer through the Straits of Fram or Nares, eventually melting in the warmer waters of the Atlantic Ocean.
"This old, thicker ice is what we hope to provide stability to the Arctic sea ice system, as we hope that the ice is not as vulnerable to melting as thinner, younger ice," said Alek Petty, a sea ice researcher. in Goddard. "As the ice in the Arctic becomes thinner and more mobile, the likelihood of rapid ice loss in the summer increases."
Despite the fact that this year's melt season will begin with a low extent of sea ice in the winter, this does not necessarily mean that we will see another record low in summer.
"A lot will depend on the wind and temperature conditions in the spring and summer," Parkinson said.
As of March 22, Operation IceBridge, NASA's aerial survey of polar ice, is hovering over the Arctic Ocean to map the distribution and thickness of sea ice. In the fall, NASA will launch a new satellite mission, Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2), which will continuously monitor how the thickness of sea ice is changing in the Arctic.
For NSIDC analysis: http://nsidc.org/arcticseaicenews/2018/03/arctic-sea-ice-maximum-second-lowest/