WASHINGTON Even before the dawn of agriculture, people may have caused the planet to warm up, a new study suggests.
Mammoths used to roam modern-day Russia and North America, but are now extinctand there's evidence that around 15,000 years ago, early hunters had a hand in wiping them out. A new study, accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union (AGU), argues that this die-off had the side effect of heating up the planet.
"A lot of people still think that people are unable to affect the climate even now, even when there are more than 6 billion people," says the lead author of the study, Chris Doughty of the Carnegie Institution for Science in Stanford, California. The new results, however, "show that even when we had populations orders of magnitude smaller than we do now, we still had a big impact."
In the new study, Doughty, Adam Wolf, and Chris Fieldall at Carnegie Institution for Sciencepropose a scenario to explain how hunters could have triggered global warming.
First, mammoth populations began to dropboth because of natural climate change as the planet emerged from the last ice age, and because of human hunting. Normally, mammoths would have grazed down any birch that grew, so the area stayed a grassland. But if the mammoths vanished, the birch could spread. In the cold of the far north, these trees would be dwarfs, only about 2 meters (6 feet) tall. Nonetheless, they would dominate the grasses.
The trees would change the color of the landscape, making it much darker so it would absorb more of the Sun's heat, in turn heating up the air. This process would have added to natural climate change, making it harder for mammoths to cope, and helping the birch spread further.
To test how big of an effect this would have on climate, Field's team looked at ancient records of pollen, preserved in lake sediments from Alaska, Siberia, and t
|Contact: Maria-Jose Vinas|
American Geophysical Union