Worries about Global Warming and a New Ice Age

While policymakers have worried long and hard about global warming, which might raise Earth's temperature 1.4 to 5.8 degrees C by century's end, a growing body of evidence suggests natural forces could just as easily plunge Earth's average temperatures downward. In the past, the planet's climate has changed 10 degrees in as little as 10 years.

A more timely test of the North Atlantic's role in abrupt climate change, they say, may come through unraveling the mystery of a rapid cooling event that peaked 8,200 years ago.

By the standards of the Little Ice Age, the 8,200-year event was frosty and global. Although the event lasted only about 100 years, Greenland's temperatures dropped by about 3 degrees C. Indeed, the consultants who argue for upgrading the national security status of abrupt climate change used this event as their model.

Graphic - Changes are abrupt and during last 450,000 years the Earth is usually colder.