At the top of the world, the Arctic Ocean is covered by a floating cap of ice that represents one of the most obvious indicators of global climate change. The sea ice is a semi-permanent feature that grows in the winter and shrinks in the summer. But the minimum ice extents and volume that occur at the end of summer have been getting lower and lower. Warmer oceans and a warmer atmosphere are the basic reasons behind these reductions. 2015 has just produced the fourth-lowest sea ice extent on record, and satellites have been measuring sea ice extents since 1979.
The loss of Arctic sea ice is a big deal – ask anyone who lives next to an ocean. Water has an amazing capacity to absorb (and later re-release) large amounts of heat, and moderate the climate. Reduced sea ice cover also means that more solar radiation is absorbed, instead of being reflected back out by the ice and the snow. In the Arctic, these factors work together to amplify the CO2-induced warming.
The National Snow and Ice Data Center (NSIDC) has compiled daily sea ice extents from multiple satellites. I wrote a little R script that grabs all the daily data from their FTP server, extracts the annual minimum, and calculates decadal means. Then, I went hunting for some music* to accompany the results.
The minimum ice extent in 2015 was 4.31 km², a whopping 38% lower than the average minimum extent in the 1980’s (6.96 km²). The top-selling album of the 1980’s (and of all time, with over 42 million copies sold) was Thriller by Michael Jackson. The timing on the video entry here is fortuitous and completely intentional:
Top-selling album of the 1990’s? Shania Twain, Come on Over?! Well, get your out your pleather and rock the CanCon, because the minimum sea ice extent in 2015 was 32% lower than in the glorious 90’s (6.42 km²):
Finally, we get to the first decade of the 21st century. I will admit to being surprised by both top selling album of 2000s (Hybrid Theory by Linkin Park), and the fact that ice extents in 2015 were 21% lower than the 2000 – 2009 mean (5.47 km²). In the end (pun intended), the decline of Arctic sea ice is dramatic and compelling evidence of global climate change.
*Having to lay myself some ground rules here, I do not include compilations or reissues. Which is unfortunate because the Beatles 1 was technically the bestselling album of the 2000s, but Linkin Park wins instead.