The long, alarming decline in sea ice in the Arctic


In 2020, there were many significant weather and climate events in the Arctic Ocean and surrounding seas.

A prolonged heat wave over Siberia in spring caused the sea ice in the eastern Siberian and Laptev Seas to melt rapidly.

The Arctic Ocean ice cover melted down to the second lowest minimum extent by the end of the summer since records started.

The annual freeze-up of sea ice got off to a late and slow start in the fall.

However, every single month, season, or even year is just a snapshot.

The long-term outlook is far more telling and worrying.

Forty years of satellite data indicate that 2020 was just the latest component of Arctic sea ice’s decades-long collapse.

Polar researchers Julienne Stroeve and Dirk Notz discussed some of the following developments in a study of the scientific literature: In addition to declining ice cover, melting times are becoming longer and sea ice is losing its longevity.

An progressively earlier onset of spring melt and an increasingly later onset of fall freeze-up are the result of the longer melting times.

The above map indicates trends in the onset of freezing between 1979 and 2019.

The beginning of freezing occurs roughly one week later every decade on average in the Arctic Ocean.

Since satellite records started in 1979, this equates to about a month later.

“ice-albedo feedback.”ice-albedo.

90 percent of the solar energy that falls on it is absorbed by open ocean water; bright sea ice represents 80 percent of it.

More heat can be consumed as greater regions of the Arctic Ocean are exposed to solar energy early in the season – a pattern that increases melting. Sea ice does not re-grow until this heat escapes into the atmosphere.

Another way the Arctic is shifting is seen in the diagram above: The average age of the sea ice is getting younger.

Most of the ice covering the Arctic Ocean was more than four years old when satellite records began.

Most of the ice that covers the Arctic Ocean today is “annual ice” – ice that forms in winter and does not withstand a single melting season in summer. (The remaining ice converts to biennial ice status each September after sea ice reaches its minimum extent.)
Arctic sea ice, along with some older ice that has been thinned by warm ocean water, is dominated by thin, single-year ice and is becoming more fragile.

Ships could safely navigate the North Sea route in ice-free waters in the summer of 2020 and even reach the North Pole without much resistance.

Luckily, summers are not fully ice-free yet. “We’ve been moving around 4 million square kilometers of Arctic sea ice every summer for some time,” said Stroeve, a University of Manitoba researcher. She added that when the summer ice cover falls to a new baseline of 3 million square kilometers, she plans to research what conditions and processes could push sea ice to its next “precipitous fall”

Images by Joshua Stevens of NASA Earth Observatory, using data from the National Snow and Ice Data Center courtesy of Julienne Stroeve/Polar Observation and Modeling Center (CPOM).


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