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.