In a paper published today in Geophysical Research Letters, climate scientists have estimated the distribution and trends for the Arctic icecap from 1980 through March 2011. What they have found is a significant decline in older ice on top of an overall declining trend that showed a strong but partial recovery since 2008. The graph below, from the paper, illustrates clearly these trends.

What this means for the icecap itself remains unclear. As the scientists themselves note in their conclusion:

The 32‐year record of estimated sea ice age points to a considerably younger ice pack than existed as recently as a decade ago, highlighting a net long‐term decrease in multi-year ice extent and the extent of the oldest ice types. Since older multi-year ice is typically thicker than younger ice, this translates into an overall thinner ice cover. The recovery in multi-year ice extent through March 2011 from the extreme reductions in 2007 and 2008 along with the continued aging of the surviving ice through multiple melt seasons is consistent with an ice pack that has not passed a tipping point across the Arctic Ocean as a whole, and reflects favorable large‐scale ice transport patterns conducive to retaining multi-year ice. . . . A key question then is whether the increases in the extent and age of the multi-year ice seen over the last three years can be sustained ‐ continuing the recovery observed since the 2007/2008 record minima and thickening enough to become less vulnerable to another extreme melt season. [emphasis mine]

The data gathered by numerous scientists over the past three decades — reinforced by this paper — clearly shows that during that time period the Arctic icecap has been shrinking slowly in size. It also shows that since 2008 (the time period corresponding to the sun’s recent prolonged and deep sunspot minimum), the icecap showed some recovery.

In other words, Al Gore’s prediction from 2009 that the icecap will be gone “in just a few years” remains as stupid and unlikely as it ever did. The icecap might be shrinking, but the trends have all not been downhill, and they are certainly too slow to have the icecap disappear that quickly.

The authors noted the following about this recent recovery:

One likely reason for the recent increase in multiyear ice extent was a shift toward a more “ice favorable” atmospheric circulation. . . . Strong and sustained negative Arctic Oscillation (AO) periods during winter not seen since the late 1960s were present in 2010, with an annual mean AO index of −1.04. This was the lowest annual mean from 1950 through 2010, over two standard deviations from the mean of −0.14, and one of only three years with a negative AO in 11 of the 12 months. The year 2010 was also unusual as the only year over the same period with a negative North Atlantic Oscillation (NAO) in all months, with an annual mean NAO index of −1.30; the lowest observed over the 61‐year period and more than three standard deviations less than the long‐term mean of −0.10.

Why the AO and NAO were both so negative (cold) remains unexplained. No direct link to the sun yet exists, though the timing coincidence is intriguing and some scientists have theories.

Moreover, if you look closely at the graph, you can see that almost all the decline involved older ice, five years old. Ice two and three years old did not show any significant trends, either up or down, while four year old ice only showed a significant decline after 2007. This suggests that while the icecap has shrunk, it is far from disappearing. Instead, it appears to be recycling itself more quickly.

Whether this loss of older ice has anything to do with warmer temperatures also remains unproven, as far as I can tell. The evidence of a warming trend in the last three decades remains inconclusive, with satellites showing no warming in the past decade while the ground-based data showing a warming since the 1940s. Unfortunately, this ground-based data remains untrustworthy because its compiler, Phil Jones of the Climate Research Unit, did not keep good records and indicated a willingness to fudge that data for his own political interests, as shown in the climategate emails.

And even if there has been a warming trend, linking it to the change in the icecap remains difficult and somewhat unclear. Why should only older ice disappear if the climate was warming? One would think that newer ice, less compact and usually forming in the warmer parts of the icepack, would be the first to disappear during a warming trend.

Once again, the data suggests that we really won’t know what is happening until we get at least another decade or so of data. And even that might be too soon.