A Condensed Look at ?Arctic Sea Ice Decline: Faster Than Forecast??
7 May, 2007 12:31 pm
A new study indicates that the Arctic Ocean is losing its sea ice cover faster than is captured by the most advanced models used in the 2007 report by the Intergovernmental Panel on Climate Change (IPCC).
The authors compared the last fifty years of sea ice observations with output from the eighteen IPCC climate models, and found that none of the models captured the observed trend during September (the end of the summer melt season) of -7.8 percent per decade. On average, the models suggest a trend that is three times smaller, at –2.5 percent per decade. The fastest rate of September retreat in any individual model simulation was -5.4 percent per decade, which is still thirty percent slower than scientists observed.
Currently, the observations indicate sea ice conditions for September are about thirty years ahead of where the models say we should be. Thus, it is entirely likely that a seasonally ice-free Arctic state may well occur during the first half of this century.
Stroeve and her co-authors speculate that the computer models may fail to capture the full impact of increased carbon dioxide and other greenhouse gases in the atmosphere. Results from this study suggest about half of the ice loss from 1979 to 2006 is caused by human activities (e.g. greenhouse gases) and the other half is caused by natural variability in the climate system. However, if the models are under-representing the human-induced climate response, greenhouse gases may be playing a significantly greater role.
The discrepancy between the models and the observations is not necessarily an indication of poor models, but rather is an indication of the complexity of change in the Arctic, and the difficulty of accurately modeling such change. Although the models used in the IPCC report incorporate many improvements compared to earlier climate models, shortcomings remain, such as the models ability to accurately model the vertical structure in the ocean and oceanic heat transport. Recent studies indicate that the transport of heat from the sub-polar oceans to the Arctic waters is playing a larger role than previously thought in melting the sea ice. This contribution to melting of the Arctic ice pack is underestimated in our current models.
Although it remains a mystery as to the exact date when the Arctic may become ice free in summer and how rapid this transition may be, this new state would have profound implications for climate around the globe. The snow and ice at the poles help keep our planet cool by reflecting most of the incoming solar energy from the sun back out to space. As the amount of snow and ice decreases, the Earth’s surface absorbs more solar energy, furthering snow and ice melt and resulting in more warming. A warmer Arctic will result in altered atmospheric and oceanic circulations that will affect weather worldwide. Studies have already linked Arctic sea ice loss to changes in atmospheric patterns that cause reduced rainfall in the American West and increased precipitation over western and southern Europe.
Already, the loss of sea ice has had adverse effects for the people and wildlife in the Arctic that depend on the sea ice for their livelihood. The complete disappearance of the summertime sea ice will leave the polar bear, ring seals and other Arctic creatures without habitat, and will have a profound impact on the people who live in the Arctic.
Stroeve, J., et al. (2007), Arctic sea ice decline: Faster than forecast, Geophys. Res. Lett., 34, L09501, doi:10.1029/2007GL029703.