The news media releases on Arctic sea ice continue, with caveats buried deep in the articles, if at all. An example of the latest release is from the BBC on September 28th entitled “Arctic ice ‘disappearing fast’.” No mention is made of the need to reconcile the National Snow and Ice Data Center (NSIDC) Arctic sea ice information with that of the University of Illinois data (see http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.anom.jpg for their analysis of long-term trends). The University of Illinois shows the largest negative deviation from the long-term average in 1995. There is no question that there is a long-term decline in areal coverage (since 1973, as we have also documented in Pielke et al. 2003 , which is the time period we have reasonably robust areal coverage data from satellites), and that human climate forcings of all types must be playing some role, however, its temporal trends are more complicated than discussed in the BBC and other media articles.
As the BBC article summarizes,
“If the current trend can be ascribed in part to human-induced climate change, Mark Serreze sees major reasons for concern.
‘What we’re seeing is a process in which we start to lose ice cover during the summer,’ he said, ‘so areas which formerly had ice are now open water, which is dark.’
‘These dark areas absorb a lot of the Sun’s energy, much more than the ice; and what happens then is that the oceans start to warm up, and it becomes very difficult for ice to form during the following autumn and winter.’
‘It looks like this is exactly what we’re seeing – a positive feedback effect, a ‘tipping-point’.”
The idea behind tipping-points is that at some stage the rate of global warming would accelerate, as rising temperatures break down natural restraints or trigger environmental changes which release further amounts of greenhouse gases.
Possible tipping-points include:
• the disappearance of sea ice leading to greater absorption of solar radiation
• a switch from forests being net absorbers of carbon dioxide to net producers
• melting permafrost, releasing trapped methane.
This study is the latest to indicate that such positive feedback mechanisms may be in operation, though definitive proof of their influence on the Earth’s climatic future remains elusive.
We have examined the consequences of the removal of Arctic sea ice on summer climate in the Arctic in “Earth System Modeling- An Integrated Assessment Tool for Environmental Studies”. Glen Liston and Joseph McFadden of our research group ran the Regional Atmospheric Modeling System (RAMS) for June 1995 with assimilated observed sea ice and with the ice removed. What we found was that near-surface air temperatures are actually warmer over the Arctic Ocean (by over 1 degree Celsius) when the sea ice is present! The reason for the warming is that sea ice absorbs solar radiation and transfers some of this energy as sensible heat back into the atmosphere. Without the sea ice, while the ocean gains heat, the atmosphere is cooler. The difference in surface air temperature, with and without Arctic sea ice, is communicated to the atmosphere which could then alter tropospheric circulation patterns. Until the ocean warms enough through the addition of heat that is not present with the sea ice cover, the summer air temperature warming would be muted. This negative summer feedback is one example of the complexity of the Arctic climate with respect to both natural climate variability and human-caused climate change which has been ignored in the media releases.
This coming winter will provide an effective additional scientific test of whether the Arctic sea ice will continue to decline in areal coverage. A return to the larger winter coverage of earlier years will bring into question the statement of the BBC that “Arctic ice ‘disappearing fast’.” If the winter coverage repeats last year’s record low, however, than there will be support for the conclusions provided in the news release and of the NSIDC conclusions. Fortunately, in the case of Arctic sea ice coverage, we have a testable hypothesis in a reasonably short period of time. We will revisit this issue this winter. Meanwhile, we look forward to NSIDC and the University of Illinois reconciling their data, so a true scientific consensus can be achieved on this subject. Even the BBC caveats their conclusions,
“This study is the latest to indicate that such positive feedback mechanisms may be in operation, though definitive proof of their influence on the Earth’s climatic future remains elusive.”
The behavior of Arctic sea ice this winter and over the next few years provides data to more definitively address these issues.