When will the next ice age occur?
Glen Ridge, N.J.
If historical patterns repeat themselves, within about 2,000 years. But that's an extremely big "if." Over the past several million years, Earth has spent most of its time sheathed in ice. But about every 100,000 years, the planet thaws. These warm spells, called interglacial periods, usually last between 15,000 and 20,000 years. We've been enjoying our current interglacial period for about 18,000 years-giving us roughly 2,000 to go before the next deep freeze.
Many factors may affect this pattern, however, and scientists disagree on the impact of these influences. First, we're still learning about all the natural cycles that affect Earth's climate. These include astronomical forces such as variations in sunspots, the planet's tilt, and tectonic pressures such as shifting landmasses and volcanic activity.
Also, we're still assessing the effect of our own impact on climate. Increased carbon dioxide and other greenhouse gases have been proven to increase surface temperatures. Ulrike Lohmann of Dalhousie University, in Halifax, Nova Scotia, which co-sponsored a conference on "Global Warming and the Next Ice Age" in 2001, predicts the icy arrival in about 10,000 years. Predictions from other scientists vary from 5,000 to 50,000 years.
Edited by Bob Sillery
Research by Brad Dunn and Michael Moyer