The Arctic Sea freezes over. The Arctic Sea melts. This happens every year. The average date for the maximum extent of Arctic Sea ice, based on a period of 1981-2010, is March 12. The minimum extent is reached, on average, about September 15h.
Every year for the last several years, the minimum ice has been much lower than average in extent, and many years in a row have seen record minima. This is considered to be the result of global surface warming caused by human release of greenhouse gas pollution.
It is said that we can’t use the maximum ice cover to predict the minimum ice cover very accurately, because a lot of things can happen to affect the total ice cover during those many months of melting. However, the maximum ice amount for, say, 1979-1988 (the first ten years for which we have really good data on this) was high compared to the last ten year period, and correspondingly, the minimum extent was greater for that first ten year period than the most recent ten years, so there is a correlation. Still, the date of the maximum extent has tended to not move around much, and the same is true for the date of the minimum extent.
Bt maybe not this year. This year’s maximum Arctic Sea ice extent seems to have flatlined at a record low value, as shown in the graph above, from here. The current sea ice extent is that red line all by itself down near the bottom.
It may well be the case that the sea ice will start to re-freeze, and this line will go up again over the next two weeks or so, and max out near the historical average. The next week or so should be below freezing across much of the Arctic Sea, but there is a warm intrusion near Greenland and Europe, with above freezing air, expected to persist for that entire time. Overall, warm air and ice-breaking-up storms have invaded the Arctic repeatedly this winter. The sea ice extent may recover over the next several days, but I get the impression that most experts are quietly thinking it won’t.
This is not terribly surprising, given that the Earth’s surface temperatures are increasing, and sea ice is decreasing. This year, a El Ninño is adding fuel to the fire, as it were, and making these conditions even more extreme.
A concerning possible outcome is this: The Arctic Sea ice helps cool the planet by reflecting away sunlight. It is a reasonable assumption that during summers with much less ice, there is much less cooling. This can have impacts on the longer-lived fast ice* that is also melting in the arctic, and on nearby glaciers in greenland, and the planet overall. This is what is known as a “positive feedback” which is a somewhat misleading term, because this is not an especially “positive” event.
*CORRECTION: My friend and colleague Tenney Naumer, who watches both the weather and the Arctic very closely, contacted me to let me know that the “fast ice” is long gone. She told me, “In 2012, the ice in the channel between Ellesmere and Axel Heiberg Island (to the south of Ellesmere) melted out — that is the place where the ice had existed for more than 10,000 years. The Ward Hunt Ice Shelf broke off in 2002. The Ayles Ice Shelf broke off in 2005. In 2007, I watched (here) the ice break away from most of the Arctic side of the archipelago, and it has been all downhill since. It’s all gone now.”