The Arctic Ocean one year ago to this date. Photo: US Geological Survey via flickr
Perhaps you don't need more convincing that whether a given year sets a new record or not Arctic sea ice is on the decline, but maybe you do: Climate Progress highlights a study in Quaternary Science Review which confirms that human activity is driving changes in ice cover, and furthermore that there's now less ice in the Arctic that at any point in recent geologic history.CP asked study lead author when was the last time the Arctic was ice-free. Leonid Polyak responded, with the caveat that paleo data is "very scant",
...The next best (actually, better) candidate is the Last Interglacial, about 125,000 years ago, again due to orbitally driven high insolation: The ice was likely very low, but we can't say whether it was completely ice free in summer or not. There are are also a few other major interglacials, which may have had a similar picture, in particular Marine Isotopic Stage 11, about 450,000 years ago. In any case we are talking about very rare events controlled by a forcing very different from today. If none of those intervals was really ice free, then a million year assessment would be correct.
Which is an elaboration on what Polyak's paper states:
The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.
As is usual, Climate Progress goes into to excruciating detail on the subject--also reminding readers that the temperature increases in the Arctic are higher than the average for the Northern Hemisphere by a factor of 3-4--so check it out if you're so inclined to dig deeper: Climate Progress
UPDATE: As Climate Progress' Joe Romm kindly pointed out, in the original headline of this post I conflated some details in the midst of all his excruciating detail and wrote a misleading headline. Ice in the Arctic is lower now that in thousands of years, but was probably lower still between 6000-10,000 years ago. The last time the Arctic was likely ice-free was 100,000+ years ago, which is the direction we're heading right now--this time not due to natural variations, but due to human activity. Apologies.
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