The minimum extent of Arctic sea ice has dropped to 4.72 million square kilometers in 2021.
The yellow line shows the minimum extent of Arctic ice between 1981-2010. (Photo: Nasa)
Sea ice in the Arctic has hit the annual minimum extent after disappearing in the 2021 Northern Hemisphere spring and summer. Satellite observations indicate that the current ice cover in the region is 12th-lowest on record as the minimum extent of Arctic sea ice dropped to 4.72 million square kilometres.
The average September minimum extent record shows a significant decline since satellites began measuring ice cover in 1978. The last 15 years (2007 to 2021) are the lowest 15 minimum extents in the 43-year satellite record, Nasa said adding that sea ice extent is defined as the total area in which ice concentration is at least 15 per cent.
Sea ice acts as a lid on a pot of boiling water, which when removed leads to heat and steam escape into the air. Researchers say that the region is getting more heat and moisture from the ocean going into the atmosphere leading to a jump in warming. This warming and moistening of the atmosphere slow down the vertical growth of the sea ice, making it more vulnerable to melt in the summer months.
Nasa said that sea ice does not raise global sea levels directly, still, a shrinking Arctic sea ice extent can expose relatively warm seawater to the region’s coastal ice sheets and glaciers, causing more melting that contributes freshwater to the ocean and does cause sea-level rise.
Apart from having an impact on the global sea level the Arctic ice also has a great deal of influence over clouds in the sky, which help in predicting how much and how fast the Arctic will continue to warm in the future. Clouds have the capability to both warm and cool the surface below them. Researchers have now found that by releasing heat and moisture through a large hole in sea ice known as a polynya, the exposed ocean fuels the formation of more clouds that trap heat in the atmosphere and hinder the refreezing of new sea ice.
The study has allowed scientists to more accurately spot how cloud formation changed near the ocean’s surface and near the surrounding sea ice.
“Instead of relying on model output and meteorological reanalysis to test our hypothesis, we are able to pull near-instantaneous satellite scan data from the area near the polynya. Since each scan is collected over a time scale on the order of about 10 seconds, it is more likely the polynya and nearby ice are experiencing the same large-scale weather conditions, so we can more accurately tease apart what effect the change from the ice surface to the water surface is having on the overlying clouds,” Emily Monroe, an atmospheric scientist at Nasa explained.
The new research shows clouds over the polynya emitted more heat than clouds in adjacent areas covered by sea ice. Those low clouds contained more liquid water, too—nearly four times higher than clouds over nearby sea ice.
Nasa said that the team is planning to take their research to the next level and test whether a similar cloud effect can be observed in other areas where sea ice and open ocean meet.
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