According to data just now available, the total surface area of the summertime Arctic Sea that is covered in ice has reached the lowest point ever recorded.

Every (northern) summer the sea ice in the Arctic melts to some degree, reaching a minimum around the middle of September. Over the last several years, the amount of ice at this minimal point has been lower than previously recorded. Accurate records go back only a few decades, so this shift in ice cover reflects only the most recent period of Anthropogenic Global Warming (AGW).

Today, I got an email from my colleague John Abraham (the John Abraham from this podcast) noting that this morning’s data indicated that the ice had reached this minimum extent, as shown in this graph from the Arctic Sea Ice Monitor:

From the Arctic Sea Ice Monitor. "The latest value : 4,189,375 km2 (August 24, 2012)"

It is now August 24th, so there are about three weeks, more or less, of melting still to come. Therefore, we can say with some confidence that we will in the end have the smallest extent of ice so far in this data set.

With so much of the sea exposed, the water itself will warm from sunlight which would otherwise be reflected away by the shinier ice and snow … the albedo of the arctic is at a long-tem low because of this melting. Some people feel, and it is just a guess at this point, that the date of minimum ice extent might be getting later, moving towards late September from mid September. Statistically, this can not be said to be true at this point, but it does make sense that with less ice, there can be a warmer sea, and thus a slower re-start to the Arctic Ocean icing over again. Over the next few years we may well see the average date of sea ice minimum, which is a number with a lot of variation so this will be hard to detect, move later.

I’ve recently discussed the overall pattern of melting in the Arctic, and just yesterday I posted a piece on global warming and sea level rise in the Daily Kos Blogathon, and of course, melting ice (but mainly continental glacial ice) is key to that. Also, I hear last night that Al Gore and some of his colleagues will be posting at that Blogathon this morning, so go check that out.