The story so far: The Arctic winter sea ice hit its maximum extent on February 25 this year, according to the data collected by the United States National Snow and Ice Data Centre (NSIDC). This is the tenth-lowest in the satellite record maintained by the NSIDC, a Distributed Active Archive Centre of National Aeronautics and Space Administration (NASA).
Arctic sea ice extent peaked at 14.88 million square kilometres, according to the data analysed by the NSIDC. This is around 770,000 square kilometres below the 1981-2010 average maximum, equivalent to an area of ice slightly larger than the U.S. states of Texas and Maine combined.
Since February 25, the extent of Arctic sea ice has dropped around 390,000 square kilometres. The loss of sea ice has primarily been observed in the Sea of Okhotsk and the Barents Sea. The losses, however, have been offset by gains in the Bering Sea, Baffin Bay, and the Labrador Sea, according to NSIDC. At the same time, gains in the Antarctic sea ice are not enough to balance the loss in Arctic sea ice.
What is sea ice?
Sea ice is essentially frozen ocean water. All stages of winter sea ice – formation, growth, and melting – occur in the ocean, unlike icebergs, glaciers and ice shelves that originate on land.
Sea ice in the Arctic usually reaches its peak in March. The minimum extent is usually recorded in September after it melts through the warmer months. The Antarctic sea ice in the south follows the opposite cycle.
According to NASA, the maximum extents of the sea ice in the Arctic have declined at a pace of about 13% per decade since 1979 – when satellites began reliably tracking the data. This is in sync with human global warming activities like emission of carbon dioxide, deforestation, and so on.
Why is polar sea ice important?
Polar sea ice is important to maintain global temperatures.
Sea ice reflects 80% of the sunlight that strikes its surface, thus keeping the polar regions cool. Once the ice melts in the summer, the dark surface of the ocean is exposed and it absorbs 90% of the sunlight that falls on it. This causes a rise in the temperature of the polar region. Small temperature changes at the poles can lead to greater warming over time, making polar regions extremely sensitive to climate change. The loss of sea ice can accelerate global warming.
How is the extent of sea ice measured?
The extent of sea ice in an area of the ocean is where there is at least some ice. Scientists usually use a 15% cutoff as the threshold of minimum concentration to mark the ice edge. This has been observed to provide the most consistent agreement between satellite and ground data.
In the past, NSIDC has used NASA’s Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E) on the NASA Aqua satellite and the Special Sensor Microwave/Imager (SSM/I) instrument on the Defence Meteorological Satellite Program (DMSP) satellite to observe the extent of sea ice. These satellites collect data when they pass over the polar regions multiple times during the day and the data is then transformed into images for analysis. The AMSR-E satellite is no longer functioning.
What is NSIDC?
NSIDC researches the earth’s cryosphere – all things snow, ice, glaciers, and frozen ground. It began functioning in 1976 when the United States Geological Survey transferred responsibility for the World Data Centre for Glaciology to National Oceanic and Atmospheric Association Data and Information Service.
- Sea ice is essentially frozen ocean water. All stages of winter sea ice – formation, growth, and melting – occur in the ocean, unlike icebergs, glaciers and ice shelves that originate on land.
- According to NASA, the maximum extents of the sea ice in the Arctic have declined at a pace of about 13% per decade since 1979.
- Polar sea ice is important to maintain global temperatures.
Published - April 01, 2022 12:43 pm IST
