Arctic Sea Ice: the Chicken or the Egg?

Melting sea ice in the Arctic is claimed to be one of the major signals that man is dangerously warming the planet. Indeed, one of the more amusing episodes of the global warming chronicles was the discovery of open water at the North Pole, which the New York Times claimed had not been seen for 50 million years. It had to retract the story, of course, because open water at the North Pole in the summer is not unusual. It is becoming less and less clear, however, whether melting Arctic sea ice is a symptom of warming temperatures or the cause.

A study in the Journal of Climate (September 2002) finds that global warming is not the cause of melting sea ice, but that melting sea ice is causing the warming. Changes in sea ice extent, it turns out, are related to the well known phenomenon known as the Arctic Oscillation (AO) index, which is a measure of atmospheric circulation in the Arctic. Much of the observed thinning in the Arctic is due to changing wind patterns that rearrange the sea ice. When the AO index is in its positive phase, sea ice thins and retreats; in its negative phase it thickens and advances. The AO is an entirely natural process for which we have measurements for the last 100 years. Its current values are about the same as they were 100 years ago.

The study concludes, "Intuitively, one might have expected the warming trends in SAT [surface air temperature] to cause the thinning of sea ice, but the results presented in this study imply inverse causality; that is, that the thinning ice has warmed SAT by increasing the heat flux from the ocean." In other words, a change in the AO index thins the ice which exposes the warmer ocean water to the cold air and warms it. It turns out that melting Arctic sea ice is responsible for Arctic warming, not the reverse.

The Cooler Heads Coalition will hold a screening of The Climate Conflict, on October 7, from 3:15 to 4:15 p.m., in Room 385 of the Senate Russell Office Building. The Climate Conflict is an award-winning Danish documentary about the global warming debate in general and about the role of solar variability in particular. Although it has won six awards in Europe and has been shown on major networks in most European countries, no American network or station has picked it up. Our special screening will be introduced by Dr. Paal Brekke of the European Space Agency, who is also interviewed in the film.