As we approach the time of year of the peak of areal coverage of Arctic sea ice and the minimum areal coverage in Antarctic sea ice, Climate Science is presenting a status report based on the excellent data analysis provided at the University of Illinois website The Cryosphere Today. The coverage for January 31 2008 is about 900,000 square kilometers below average for the Arctic [Northern Hemisphere] (see) and about 500,000 square kilometers above average for the Antarctic [Southern Hemisphere] (see). The Illinois website has also introduced an effective display of past Arctic sea ice coverage at the same time of the year (see Compare Daily Sea Ice).
What has not been discussed, however, with respect to the global sea ice coverage is the relationship to albedo weighted by the time of year (i.e., an insolation-weighted albedo). We presented this concept in our papers
Pielke Sr., R.A., G.E. Liston, and A. Robock, 2000: Insolation-weighted assessment of Northern Hemisphere snow-cover and sea-ice variability. J. Geophys. Res. Lett., 27, 3061-3064.
Pielke Sr., R.A., G.E. Liston, W.L. Chapman, and D.A. Robinson, 2004: Actual and insolation-weighted Northern Hemisphere snow cover and sea ice — 1974-2002. Climate Dynamics, 22, 591-595 DOI10.1007/s00382-004-0401-5.
In our second paper, the abstract reads
“Actual and insolation-weighted Northern Hemisphere snow cover and sea ice are binned by latitude bands for the years 1973–2002. Antarctic sea-ice is also analyzed for the years 1980–2002. The use of insolation weighting provides an improved estimate of the radiative feedbacks of snow cover and sea-ice into the atmosphere. One conclusion of our assessment is that while a decrease in both areal and insolation weighted values have occurred, the data does not show a monotonic decrease of either Arctic sea-ice or Northern Hemisphere snow cover. If Arctic perennial sea-ice is decreasing since the total reduction in areal coverage is relatively small, a large portion of it is being replenished each year such that its radiative feedback to the atmosphere is muted. Antarctic sea-ice areal cover shows no significant long-term trend, while there is a slight decrease in the insolation-weighted values for the period 1980–2002. From the early 1990s to 2001, there was a slight increase in both values. The comparison of general circulation model simulations of changes over the last several decades to observed changes in insolation weighted sea-ice and snow cover should be a priority research topic.”Unfortunately, the IPCC did not make such an assessment (of insolation-weighted albedo) a priority.
With the data now available up through January 2008, it is clear that the global sea ice insolation-weighted albedo, using the methodology in our papers, is a global average negative radiative feedback at present (January 2008), as the above average sea ice coverage in the summertime in the Antarctic dominates this climate metric in the global average. This feedback is larger also since the Earth is closer to the Sun in January. If the Arctic sea ice areal coverage is again lower this northern hemispheric summer, this would be a global average positive radiative feedback.
Climate Science recommends the presentation of this insolation-weighted albedo on website such as at the University of Illinois and the National Snow and Ice Data Center.