Are sea-ice driven increases of absorbed solar radiation in the Arctic offset by increasing sea ice extent in the Antarctic?: A bipolar comparison of satellite-derived estimates of absorbed solar radiation and sea ice area

Abstract:

Due to its high surface albedo, sea ice reflects a substantial amount of incoming solar radiation relative to an ice-free ocean surface. Thus the presence of sea ice results in less absorption of energy during the long days of the polar summers. AS expected, the dramatic decline in Arctic summer sea ice area over the past decades has been accompanied by an increase in absorbed solar radiation (ASR). This has been observed by in situ measurements as well as satellite observations. The Clouds and Earth’s Radiant Energy System (CERES) instrument on the NASA EOS Terra platform has provided global coverage of solar radiation since late 1999, providing a large-scale indicator of changes in absorbed solar radiation. These data show that the dramatic decrease in Arctic summer sea ice has been accompanied an increase in absorbed solar radiation during the boreal summer, with the largest gains corresponding to regions of the most notable summer ice loss. While overall there is good correlation, the relationship is far from perfect. This is not unexpected since other factors – particularly clouds – play a role in the amount of ASR.

In contrast to the decreasing sea ice in the Arctic, the Antarctic has seen a trend of increasing coverage. The increases are smaller, in both absolute and relative terms. However, the southern hemisphere sea ice cover is at a higher average latitude than in the north due to the presence of the Antarctic continent and is thus is potentially exposed to higher incoming solar radiation. Here we investigate the relationship between changes in sea ice and changes in ASR (estimated from CERES data) in the Arctic and Antarctic during their respective summer seasons. To first order, both hemispheres show an expected relationship between sea ice and absorbed solar radiation in the Arctic (sea ice decrease, ASR increase) and the Antarctic (sea ice increase, ASR decrease). However, the correlation in the Antarctic is not nearly as clear in the Arctic and the magnitude of the ASR trend is smaller, suggesting a more complicated connection between ASR and sea ice, likely due to a larger role of clouds in the Antarctic, the different characteristics of the sea ice itself, and possibly other factors