Dear EarthTalk: it has been said that global warming will bring a new ice age.

Dear EarthTalk: It has been said that global warming will bring a new ice age. Is this true or only fiction?--Nitisha Jain, Delhi, India

While no one can be sure what and how severe the effects of global warming will be, it is entirely possible that one outcome of our profligate use of fossil fuels could be an ice age. The theory goes that a warming-induced influx of cold, fresh water into the North Atlantic from melting polar ice caps and glaciers could shut down the Gulf Stream, an underwater channel of warm ocean water that winds its way north from the Caribbean and moderates temperatures in the northeastern U.S. and Western Europe.

The result, some scientists speculate, would be a return to ice age conditions. In the extreme, glaciers and freezing temperatures would render large swaths of the civilized world uninhabitable and would kill off untold numbers of species unable to move or adapt. A less dire version would still cause bitterly cold winters, droughts, worldwide desertification and crop failures, and trigger resource wars across the globe.

Of course, over the history of geological time the planet has endured vast shifts in temperature and many ice ages and subsequent warm-ups. The last major ice age peaked about 20,000 years ago, when extensive ice sheets covered large parts of what we now call North America, Europe and Asia. Many climate scientists believe the planet oscillates between warmer and colder periods without human intervention due to various factors related to its orbital path and also variations in heat output from the Sun on a millennial scale--and that we are naturally heading toward another ice age, regardless of greenhouse gas emissions, over the next several dozen millennia.

But others believe those very emissions might just save us from the freezing throes of another ice age. In a study published in the September 4, 2009 issue of the Science magazine, researchers report that human-induced climate change is quite possibly fending off what had been presumed to be an inevitable descent into a new ice age based on data collected across various Arctic regions in recent years.

The study found that after a slow cooling of less than half a degree Fahrenheit per millennium as a result of a cyclical change in the orientation of the North Pole and the Sun, the Arctic warmed by some 2.2 degrees just since 1900, with the decade from 1998 to 2008 the warmest in 2,000 years. Without human intervention, researchers would expect summer temperatures in the Arctic to cool for another 4,000 years or so as the North Pole gets further from the Sun, but in fact, researchers believe, global warming is reversing this trend.

"The slow cooling trend is trivial compared to the warming that's been happening and that's in the pipeline," reports the study's lead author Darrell S. Kaufman of the University of Arizona. Of course, only time will tell whether our relatively short-term flood of pollutants will have a pronounced long-term effect on the planet's geological-scale warming/cooling dynamic. In the meantime, most responsible individuals and governments are working to lower their carbon footprints to try to take man back out of the climate equation once and for all. Hopefully our grandkids' grandkids will be around to thank us.

CONTACT: Science Magazine, www.sciencemag.org/cgi/content/short/325/5945/1236.