We at Daily Kos are well-informed about the impacts of anthropogenic global warming, or AGW for those who love acronyms. Well, a colleague of mine here at work sent me a web cam picture (NOAA Arctic NetCam XL #1) of the North Pole taken at 03:48 UTC 7 July 2008. Note the weather is quite pleasant and sunny; 3.5°C (about 38°F) with a relative humidity of 84% (the dew point is probably at 32°F, the freezing point). That it is sunny is an important point I'll get to shortly.
The picture and some ruminations based on last summer's record minimum in polar ice cover can be seen below the fold.
Last summer's melt season was extraordinary, but not only directly because of AGW. There was an unusual large-scale atmospheric pattern that resulted in unusually warm and SUNNY weather, with a preponderance of southerly winds, over much of the Eastern Hemisphere half of the Arctic Ocean, resulting in temperatures as much as 13°F above normal in northern Siberia and nearby Alaska, and rapid ice melt. (NOTE: Whether AGW was responsible for the unusual climate patterns observed over the Arctic last summer or not, is not known.)
What we do know is that ice melt and increases in Arctic Ocean open water amplifies AGW, as the albedo (the ability of a surface to reflect solar radiation back toward space) of open ocean (6-12%) (and of melting ice (15-50%) for that matter) is considerably lower than that of sea ice (50-70%) or snow-covered sea ice (80-90%). So because of these reduced albedos, ice melt begets open water begets increased absorption of incoming solar radiation begets more ice melt. The following winter will, because of the increased heat held in the sea water, have delayed sea ice re-formation and likely a reduced sea ice maximum, if there are no short-term climate effects that would result in more favorable sea ice formation. And if weather patterns are such that there is increased direct solar radiation and warmer temperatures resulting from lower than normal cloud cover (as happened in summer 2007) we have a recipe for very rapid decreases in Arctic sea ice.
So how has the ice melt season gone so far in the Arctic, and do we know what atmospheric flow patterns might set up this summer?
The answer to the first question can be seen in this graphic, which I've linked to from the University of Colorado's National Snow and Sea Ice Data Center (NSIDC) in Boulder, CO. The Arctic sea ice maximum is typically in mid-to-late March, with melting moving apace by April. The chart shows that while we started with more sea ice than 2007 (but less than the 1979-2000 average), we quickly caught up with 2007 by mid-May and remained that way until late June 2008, but have more recently slowed to the point where the sea ice cover is a good bit higher than it was last year (by about 1.5-2 million km2).
Good news, maybe? Perhaps, but then we have this from the NSIDC from last April. Much of the ice is thinner than normal, and recently formed, leaving the ice system far more sensitive than normal to short-term changes in climate (and to AGW, of course).
Do we know what the atmospheric flow patterns will be in the Arctic this summer? Well, not really. But any significant warm anomalies will have a stronger impact because of the precarious condition of the existing sea ice. I'll be reporting on this occasionally if people are interested ... I seem to do better with this than with political science or strategy ;-).
UPDATE:Here is a picture of the age of the Arctic sea ice from the NSIDC from April 2008. The younger the ice, the thinner it likely is and the more quickly it'll melt. From the opening paragraph accompanying the graphic:
As the winter extent numbers indicate, new ice growth was strong over the winter. Nevertheless, this new ice is probably fairly thin. Thin ice is vulnerable to melting away during summer. Figures 4 and 5 indicate that relatively thin, first-year ice now covers 72% of the Arctic Basin, including the region around the North Pole; in 2007, that number was 59%. Usually, only 30% of first-year ice formed during the winter survives the summer melt season; in 2007, only 13% survived. Even if more first-year ice survives than normal, the September minimum extent this year will likely be extremely low.
There's no good way to get sea ice thickness from satellite pix, but there are now efforts ongoing in this regard.