National Geographic News
Humans are putting the brakes on the next ice age, according to the most extensive study to date on Arctic climate change.
The Arctic may be warmer than it's been in the past 2,000 years—a trend that is reversing a natural cooling cycle dictated by a wobble in Earth's axis.
Previously, researchers had looked at Arctic temperature data that went back just 400 years. (See photos of how climate change is transforming the Arctic.)
That research showed a temperature spike in the 20th century, but it was unclear whether human-caused greenhouse gas emissions or natural variability was the culprit, noted study co-author Gifford Miller of the Institute of Arctic and Alpine Research at the University of Colorado, Boulder.
By looking even farther back in time, Miller and colleagues' newest study reveals that the 20th century's abrupt warming may have in fact interrupted millennia of steady cooling.
It's "pretty clear that the most reasonable explanation for that reversal is due to increasing greenhouse gases," Miller said.
The researchers' computer climate models dovetails with field data such as sediment cores and tree rings, which "really solidifies our understanding," he said.
Eventually Earth will slip again into the pattern of cyclical ice ages, Miller added, but it may be thousands of years before that happens.
Ice Age, Interrupted
Earth's angle toward the sun changes due to a natural 26,000-year-long wobble, which causes the planet to spin on is axis like an unstable top, so that a line drawn from the axis would trace a cone in the sky.
The wobble causes Earth to make its closest pass by the sun in different months over the long term. For the past 7,000 years, Earth has passed closest to the sun in January.
This means less sunlight has been hitting the Arctic during its summertime, so the region should be cooling. (See an Arctic map.)
SOURCES AND RELATED WEB SITES