Ice-Albedo Feedback in the Arctic

The Arctic is an ocean covered by a thin layer of perennial sea ice and surrounded by land. Sea ice is frozen seawater that floats on the ocean surface. This floating ice has a profound influence on the polar environment, influencing ocean circulation, weather, and regional climate.

This animation above shows seasonal changes in landcover and Arctic sea ice from 2005-09-21 through 2006-09-20 courtesy of NASA/Goddard Space Flight Center Scientific Visualization Studio and Reto Stockli (NASA/GSFC).

On time scales of years to decades, the dominant cause of atmospheric variability around the North Pole is the Arctic Oscillation. The AO is an atmospheric seesaw in which air masses shift between the polar regions and the mid-latitudes. The shifting can intensify, weaken, or move the location of semi-permanent low and high-pressure systems. These changes influence the strength of the prevailing westerly winds and the track that storms tend to follow.

During the “positive” phase of the Arctic Oscillation, winds intensify, which increases the size of leads in the ice pack. The thin, young ice that forms in these leads is more likely to melt in the summer. The strong winds also tend to flush ice out of the Arctic through the Fram Strait. During “negative” phases of the oscillation, winds are weaker. Multiyear ice is less likely to be swept out of the Arctic basin into the warmer waters of the Atlantic.

Natural variability and global warming both appear to have played a role in sea ice decline. The Arctic Oscillation’s strongly positive mode through the mid-1990s flushed thicker, older ice out of the Arctic, replacing multiyear ice with first-year ice that is more prone to melting. After the mid-1990s, the AO was often neutral or negative, but sea ice failed to recover. Instead, a pattern of steep Arctic sea ice decline began in 2002. The AO likely triggered a phase of accelerated melt that continued into the next decade because of unusually warm Arctic air temperatures.

This color-coded map in Robinson projection displays a progression of changing global surface temperature anomalies from 1880 through 2018. Higher than normal temperatures are shown in red and lower then normal termperatures are shown in blue. The final frame represents the global temperatures 5-year averaged from 2014 through 2018. Scale in degree Celsius.

This animation displays a progression of changing global surface temperature anomalies. Normal temperatures are the average over the 30 year baseline period 1951-1980. Higher than normal temperatures are shown in red and lower than normal temperatures are shown in blue. The final frame represents the 5 year global temperature anomalies from 2015-2019. Scale in degrees Celsius. Animation courtesy of NASA's Scientific Visualization Studio with data provided by Robert B. Schmunk (NASA/GSFC GISS).

The next several slides highlight the impact of increasing absorbed solar radiation and its impact within the ice-albedo feedback loop.

Albedo indicates what percentage of the incoming solar radiation (sunlight) is reflected by a surface. The less albedo a surface has, the more energy contained in solar radiation (sunlight) is getting absorbed.

In the maps below, what you are looking at is not sea ice coverage, but the albedo of the Arctic region in the years 2001 (left) and 2018 (right). On the maps, white indicates regions with very high albedo like sea ice, while dark blue regions indicate regions of low albedo like the ocean. The sea ice extent boundary is represented by a black outline.

Sea ice has a much higher albedo compared to other earth surfaces, such as the surrounding ocean. The ocean reflects only about 6 percent of the incoming solar radiation and absorbs the rest, while sea ice reflects 50 to 70 percent of the incoming energy. Because the sea ice absorbs less solar energy, its surface remains cooler. As observed in the data below, regions within the sea ice extent boundary have higher albedo than their surrounding oceans.

Notice in the maps above that between 2001 and 2018, both the albedo of the Arctic and its sea ice extent boundary decreased significantly.

The map above displays the net change in solar radiation absorbed by the atmosphere over the Arctic from 2001 to 2019, as well as the change in sea ice extent over the same period. Map and solar radiation data courtesy of the Atmospheric Science Data Center, with sea ice extent data provided by the National Snow and Ice Data Center.

The map above shows the trend in sea ice percent coverage in the Arctic from 2001 to 2019, as well as the change in sea ice extent over the same period. Map and sea ice percent coverage data courtesy of the Atmospheric Science Data Center, with sea ice extent data provided by the National Snow and Ice Data Center.