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Satellite data of 40 years show how fast Arctic sea ice is shrinking


A new study of 40 years of satellite data show that the Arctic sea ice cover is shrinking as the melting period gets longer.

Arctic sea ice extent for December 2020 was 11.77 million sq km. Image courtesy NSIDC

Year 2020 was extraordinary for the Arctic in many ways – from unprecedented wildfires to record breaking temperatures to one of the lowest sea ice in satellite record. And it ended the year with a similar grim news – the US National Snow and Ice Data Center (NSDIC) measured sea ice at December 2020 end among the lowest in the satellite record as air temperatures for the month recorded higher than average in most areas. Throughout the summers, the entire Siberian region was going through an intense heat wave as many towns experienced record-breaking temperatures. On June 20, the Siberian town of Verkhoyansk recorded 38 degrees Celsius. (over 100 degrees Fahrenheit) – the highest temperature ever recorded in the Arctic!

But 2020 is not just one flash in the pan and things are grimmer than one year or one season. A new study of 40 years of satellite data show that the Arctic ice cover is shrinking as melting seasons are getting longer.

The sea-ice cover in the Arctic is also getting much younger, with the Arctic Ocean now primarily consisting of first-year ice, according to environment scienstists Julienne Stroeveand Dirk Notz. This is in stark deviation from the prevailing five-year-old multiyear sea ice during the early times of the satellite record. 

ALSO READ: Satellite images capture major events of 2020

Longer melting season

The continuous cycle of increasingly earlier starts to ice melting in spring and late starts freeze-up in autumn is resulting in longer melting seasons. As seen in this map above showing the trends in the onset of freeze-up from 1979 through 2019 freeze-up is happening about a week later each decade on an average, across the entire Arctic Ocean. This equates to nearly one month later since the start of the satellite record in 1979.

The phenomenon is the end-result a cycle called the “ice-albedo feedback.” Clear ocean water absorbs 90% of the Sun’s energy that falls on it while white sea ice reflects 80% of it. With the increase in the melting season, greater areas of the Arctic Ocean is exposed to the sun for a longer time, thus absorbing more heat. This is a cyclic pattern that reinforces melting.

Arctic ice shrinking

The second chart above demonstrates how the average age of Arctic sea ice is losing longevity. As we can see, when satellite records began, much of the Arctic Ocean ice was older than four years, while today most of the ice is “first-year ice” — that is ice that forms in winter and does not survive a single summer melt season.

ALSO READ: The burning Arctic, pandemics and the need for a green recovery

This is a vicious cycle – next year, the thin first-year ice is far easier to melt, especially given the longer melting period, making the sea ice pack more and more fragile.

Things were so bad in the 2020 summer that ships sailing through the region’s busiest lane along the Siberian coast made the highest number of trips, according to an analysis by the Centre for High North Logistics (CHNL) at Norway’s Nord University Business School. Some even made it to the North Pole without much resistance.

“The decline in the floating sea ice cover in the Arctic is one of the most striking manifestations of climate change,” scientists Stroeve and Notz noted. “While complete loss of the summer sea-ice cover will have far-reaching implications beyond the Arctic, the observed reductions in sea-ice thickness and coverage are already impacting the energy balance of our planet,” they added.

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