Thursday, November 13, 2008

Will the Next Ice Age Be Permanent?

November 12, 2008, 3:59 pm

Will the Next Ice Age Be Permanent?

return of the iceWill the next ice age be permanent? Here, the ice sheet on Greenland. (Credit: Andrew C. Revkin for The New York Times)

A new analysis of the dramatic cycles of ice ages and warm intervals over the past million years, published in Nature, concludes that the climatic swings are the gyrations of a system poised to settle into a permanent colder state — with expanded ice sheets at both poles.

In essence, says one of the two authors, Thomas J. Crowley of the University of Edinburgh, the ice age cycles over the past million years are a super-slow-motion variant of the dramatic jostlings recorded by a seismograph in an earthquake before the ground settles into a new quiet state. He and William T. Hyde of the University of Toronto used climate models and other techniques to assess the chances that the world is witnessing the final stages of a 50-million-year transition from a planet with a persistent warm climate and scant polar ice to one with greatly expanded ice sheets at both poles.

Their findings have stirred a lot of skepticism in the community of specialists examining ancient records of past climate changes and how they might relate to variations in Earth’s orbit and orientation toward the Sun and other factors. I’ll be adding some of their reactions overnight (I’m on the road).

The Nature paper goes on to propose that humans, as long as they have a technologically powerful society, would be likely to avert such a slide into a long big chill by adding greenhouse gases to the atmosphere. That doesn’t obviate the need to curb such emissions and the prospect of dangerous climate warming in the short run, Dr. Crowley said. But it is more evidence that like it or not, the future of conditions on Earth is likely to be a function of human actions, whether chosen or not.

The idea that human actions can dominate the climatic influence of things as grand as shifts in a planet’s orbit is hard to grasp, but quite a few climate specialist say it’s pretty clear this is the case. In 2003, I wrote an article exploring when scientists think we’ll slide into the next ice age (the conventional variety). James Hansen of NASA echoed Dr. Crowley, saying that as long as we’re technologically able, we’ll be able to keep the big ice at bay. Strange, wonderful stuff, climate science.