In the 2005 Arctic Climate Impact Assessment (ACIA) report, it was stated that:
“Over the past 30 years, the annual average sea-ice extent has decreased by about 8%… and the melting trend is accelerating”, and that “Sea-ice extent in summer has declined more dramatically than the annual average, with a loss of 15-20% of the late-summer ice coverage.”
They do caveat these statements by stating that “There is also significant variability from year to year.”
My AT786 class examined this issue. In 2004, I published a paper with Glen Liston, Bill Chapman, and Dave Robinson which concluded for the period 1973-2002 that “The sea-ice decline from 1973 is about 6%, while from 1980 the decrease to 2002 is about 3%…….the 1980-2002 observed decrease is less then the simulated decrease of actual sea-ice areal coverage reported in Global Warming and Northern Hemisphere Sea Ice Extent by Vinnokov et al. 1999. This paper was a follow up to a paper in 2000 by myself with Glen Liston and Alan Robock. One immediate question is why were these two papers not cited in the ACIA report?
Our class then examined the current state of Arctic sea ice. What is clearly evident in the data as of June-July 2005, is that Arctic sea-ice coverage is close to its long-term mean at this time of the year. After being well below average this past winter, the spring melt was slower than average. As discussed in the two papers I cite above, in terms of a warming feedback to the atmosphere through the radiative effect with respect to sea-ice coverage (the ice-albedo effect), it is the summer spring and summer areal coverage that is most critical (since in the winter with the long nights, there is little if any sunlight to reflect back into space).
The multi-year long-term trend and thickness of Arctic sea ice has also been used to claim the sea ice is melting. Indeed, this may be the case, although the data are more difficult to quantify in terms of long-term variability than areal coverage. Areal coverage, however, is the component of sea ice which has the most direct impact on the climate system through the ice-albedo feedback effect. As seen in these graphs, there is no clear trend since 1997. The melting trend is not accelerating. Moreover, a linear trend poorly captures the temporal behavior of this complex component of the climate system. If the sea-ice coverage returns to an earlier coverage, the clock is reset with respect to a linear trend.
Our conclusion is that the Arctic Systems Science report, which received so much media attention, significantly overstated the actual trends of Arctic sea-ice coverage.