Melting sea ice

Polar bears rely on sea ice to reach their seal prey. Without a large-scale reduction in the use of fossil fuels, Arctic warming and its impacts will ultimately impact the polar's bear survival.

© Robert Thorpe

9/21/2020 7:52:21 PM

A Sign of the Future: Summer 2020 in the Arctic

By Dr. Zachary Labe

Every September our eyes turn to the Arctic for what has become a grim milestone to observe the annual minimum extent of sea ice. To no surprise, 2020 is consistent with the long-term climate trends.

This year’s Arctic sea-ice extent minimum is the 2nd lowest on record in the satellite era (since 1979). However, reconstructions of past Arctic sea ice suggest this is also the 2nd lowest extent in at least the last 1,500 years. In addition to rising temperatures (known as Arctic amplification), the total thickness and area of September Arctic sea ice has decreased by almost 50% in the last few decades. Without a reduction in greenhouse gas emissions, state-of-the-art climate models continue to project the first “ice-free” Arctic summer by the mid 21st century. This will have dramatic consequences for the Arctic climate system and beyond. 

Overall, this summer’s temperatures in the lower atmosphere of the Arctic were the warmest on record due to a large high-pressure system that remained in control of the weather pattern. This high pressure contributed to abundant sunshine and warmth, especially along the coast of Siberia, which led to the formation of melt ponds on top of the sea ice. In addition, a strong Arctic cyclone formed in late July across the western Arctic. This powerful storm helped to fracture and pre-condition the sea ice in the Beaufort and Chukchi Seas (north of Alaska) for further melting later in August.

As of mid-September, this year’s sea ice has retreated to the central Arctic (north of Greenland) and with a small band of older (thicker) sea ice extending out into the Beaufort Sea (Figure 1).

Map of 9/14/2020 sea ice extent

Figure 1: Map of September 14’s Arctic sea-ice concentration, which is close to the annual minimum extent of Arctic sea ice for 2020. Data is from the JAXA 3-km AMSR2 satellite processed by the University of Hamburg.

Although it tracked closely to the all-time record minimum throughout the summer, this year’s sea-ice extent will be about 400,000 square kilometers greater than 2012 (Figure 2).

Chart of Arctic sea ice minimum for 2020

Figure 2: Daily Arctic sea-ice extent in 2012 (white line) and 2020 (red line) compared to average (blue line). Data is from the NSIDC Sea Ice Index v3 using passive microwave satellite observations.

Notably, the sea-ice edge has reached the 85°N parallel (Figure 1) with significantly less ice along the Atlantic side of the Arctic near Svalbard. In fact, 2020 has the smallest sea-ice extent ever observed in the northernmost portions of the Arctic Ocean (Figure 3).

Chart showing record low sea ice loss in the central Arctic in 2020

Figure 3: Daily extent of sea ice in the Central Arctic Ocean for each year from 1979 (dark purple line) to 2019 (light blue line). The years 2012 are 2020 are highlighted in yellow and blue, respectively. In this graph, the Central Arctic Ocean is the general area north of the 80°N parallel. Data is from the NSIDC Sea Ice Index v3 using passive microwave satellite observations.

Along with the unusually low sea-ice extent, the total volume of ice is currently close to a record low (Figure 4).

Chart of Arcttic sea ice 1979-2020

Figure 4: Daily Arctic sea-ice volume simulated for each year from 1979 [blue line] to 2019 [red line]. 2020 is indicated in yellow. Data is from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS).

Ocean temperatures have significantly increased this summer in areas where there would normally be sea-ice cover (>5°C warmer than average in some locations). As the winter refreeze begins later in September, this warmth from the ocean will escape into the lower atmosphere – thereby contributing to additional Arctic amplification.

While the annual sea-ice minimum receives the most media press coverage, it is an important reminder that changes to the Arctic are happening all throughout the year. The effects of declining sea and land ice, warming ocean and air temperatures, and thawing permafrost are occurring in all months of the year with far-reaching impacts. It is also a reminder of how much climate change has already impacted and will impact the region without a large-scale reduction in our emissions of fossil fuels. In just the last week, a new study has shown that the Arctic has quickly transitioned into a new climate away from a permanently frozen state. Future Arctic warming will also threaten the habitats of polar bear populations and could influence weather patterns in lower latitudes, such as over North America, Europe, and Asia.

Although 2020 was not a record low for sea ice, it is an ominous alarm that the long-term trends in the Arctic are clear if we do not change our actions and stand up for evidence-based science.

Dr. Zachary Labe is a postdoctoral researcher at the Department of Atmospheric Science at Colorado State University. Follow him on Twitter and visit his website.

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