Commercial: supplementary material for the Great Global Warming Swindle (1 hour). Also, you may buy the Swindle DVD (click the cover)Realclimate.org and Andrew Revkin from the New York Times seem to be very excited because the current amount of sea ice in the Arctic is pretty low on August 9th (yesterday) while the average day when the minimum is reached is somewhere around September 5th of each year.
They don't seem to understand - or they are not willing to reveal - three things.
First, the Arctic ice oscillates like a pulsating heart of a chaotic lunatic or a living animal, to be less provocative. ;-) It is absolutely normal for it to appear and disappear many times a year. The following NASA video shows the Arctic ice in 2005-2006. One annual loop from Aug 5, 2005 to Aug 5, 2006 or so is repeated thrice so that you see it from different angles. White and light blue color is ice at different temperatures.
The evolution doesn't look like a simple "sine", does it? Can you determine from the video where different seasons start and end? I can't. Ice is not forever. Get used to it.
The second, somewhat related thing they don't understand or they want to hide is that it is not shocking for a harmonic function combined with noise to reach a minimum 27 days before the minimum of the sine. If you set T=0 at September 5th, the correct sine function is:
At T=0 i.e. on September 5th, this function reaches the maximum, namely f(T)=1. On August 9th, when T=-27 days, the function equals about f(T)=0.9, only 5% of the "height" below the maximum. If the amplitude of the noise is more than 5% of the "height", i.e. of the difference between the maximum and minimum temperature or sea ice volume, and be sure it is, then it is completely normal for the minimum to occur 27 days earlier.
f(T) = cos (2.pi.T/365 days)
g(T) = f(T) + noise
Equivalently, I think that every sane person knows that it is not true that the warmest day of the year always occurs on the same day of the year. It is exactly the same problem. Four weeks of a difference are completely normal. The reliability of their prediction that there will be less ice in September than it is now is extremely low because the noise completely dominates near stationary points where the "cos" function is nearly constant. The odds are about 50:50, just like they are 50:50 for an index in 2007 to be warmer than in 2005, or any question like that. There is nothing spectacular about one answer or another.
The climate alarmists like to criticize climate realists whenever climate realists mention a cool weather event because it is just a random episode. But they are cherry-picking observations whose information value is much lower. Because the Arctic sea ice volume is an extremely volatile quantity, its "unusual" behavior is among the first ones that should be dismissed as noise.
The third thing they neglect is that the volume of sea ice doesn't depend on temperature only: it is also affected by precipitation patterns, among other things, so deducing warming out of these data would be wrong even if there were no fluctuations.
Polar bears, don't worry, be happy, the guys are simply stupid and obsessed.
And that's the memo.
Figure 1: Great Britain 20 000 years ago.
Update: In the fast comments, I link to a page with data that can be used to show that between the last glacial maximum 20 000 years ago and the holocene 10 000 years ago, the thickness of the icesheet that covered areas going up to New York was changing by two meters per decade. With this rate, a decade could be enough to eliminate the Arctic sea ice completely. Reality is actually slower than the average from the period I indicated.
Analogously, the sea level jumped by 100+ meters in the period that was 10 000 years long which is 10 millimeters per year - five times more than the currently observed rate. There is absolutely nothing unusual about currently observed trends, and if there is something unusual, it is the unusual stability in comparison with the natural rates. Whoever pretends that there is something unusual about the current observations is a populist who builds on the inability of most people to multiply and divide real numbers.