A dusty way to break the ice age spell.

Motes of floating dust may seem insubstantial, but they have the power to change the world. Computer simulations of Earth's climate suggest that atmospheric dust may have triggered repeated warm spells during the last ice age and could even have ended that glacial period more than 10,000 years ago.

From measurements of ancient particles trapped in glaciers, scientists know that the atmosphere was far dustier during the ice age than it is now. According to traditional climate theory, this dust helped maintain cool conditions by blocking sunlight. The computer simulations, which model both atmosphere and oceans, suggest a far more complex effect of dust, says Jonathan Overpeck of the National Oceanic and Atmospheric Administration in Boulder, Colo.

"The paradigm that glacial dust causes cooling is just wrong," he told attendees.

During the ice age, a large fraction of northern land was covered with bright snow, which reflected most of the sunlight that hit it. Dust is darker than snow, so extra dust in the atmosphere absorbed solar radiation that would otherwise have been reflected into space. Simulations with the added dust showed warmer temperatures over the continents than those without the dust. The scientists also reported their results in the Dec. 5, 1996 Nature.

The amount of dust in the sky varied markedly during the ice age. When the land-based ice sheets grew large, they stole water from the oceans and caused global sea levels to drop. Exposed ocean sediments were then picked up by the wind, adding dust to the sky. Overpeck and his colleagues suggest that sudden surges in atmospheric dustiness could have triggered abrupt warmings during the ice age and eventually pushed the planet out of its glacial conditions.