Washington DC (SPX) Jul 02, 2010
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 extinct-and 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 Field-all at Carnegie Institution for Science-propose a scenario to explain how hunters could have triggered global warming.
First, mammoth populations began to drop-both 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 the Yukon Territory, built up over thousands of years. They looked at pollen from birch trees (the genus Betula), since this is "a pioneer species that can rapidly colonize open ground following disturbance," the study says.
The researchers found that around 15,000 years ago-the same time that mammoth populations dropped, and that hunters arrived in the area-the amount of birch pollen started to rise quickly.
To estimate how much additional area the birch might have covered, they started with the way modern-day elephants affect their environment by eating plants and uprooting trees. If mammoths had effects on vegetation similar to those of modern elephants , then the fall of mammoths would have allowed birch trees to spread over several centuries, expanding from very few trees to covering about one-quarter of Siberia and Beringia-the land bridge between Asia and Alaska.
In those places where there was dense vegetation to start with and where mammoths had lived, the main reason for the spread of birch trees was the demise of mammoths, the model suggests.
Another study, published last year, shows that "the mammoths went extinct, and that was followed by a drastic change in the vegetation," rather than the other way around, Doughty says. "With the extinction of this keystone species, it would have some impact on the ecology and vegetation-and vegetation has a large impact on climate."
Doughty and colleagues then used a climate simulation to estimate that this spread of birch trees would have warmed the whole planet more than 0.1 degrees Celsius (0.18 degrees Fahrenheit) over the course of several centuries. (In comparison, the planet has warmed about six times more during the past 150 years, largely because of people's greenhouse gas emissions.)
Only some portion-about one-quarter-of the spread of the birch trees would have been due to the mammoth extinctions, the researchers estimate. Natural climate change would have been responsible for the rest of the expansion of birch trees. Nonetheless, this suggests that when hunters helped finish off the mammoth, they could have caused some global warming.
In Siberia, Doughty says, "about 0.2 degrees C (0.36 degrees F) of regional warming is the part that is likely due to humans."
Earlier research indicated that prehistoric farmers changed the climate by slashing and burning forests starting about 8,000 years ago, and when they introduced rice paddy farming about 5,000 years ago.
This would suggest that the start of the so-called "Anthropocene"-a term used by some scientists to refer to the geological age when mankind began shaping the entire planet-should be dated to several thousand years ago.
However, Field and colleagues argue, the evidence of an even earlier man-made global climate impact suggests the Anthropocene could have started much earlier. Their results, they write, "suggest the human influence on climate began even earlier than previously believed, and that the onset of the Anthropocene should be extended back many thousands of years."
This work was funded by the Carnegie Institution for Science and NASA.
Share This Article With Planet Earth
American Geophysical Union
All About Human Beings and How We Got To Be Here
If We Build 'Walkable' Neighborhoods, Will People Walk
Edmonton AB (SPX) Jun 29, 2010
Edmontonians love their cars. In fact, 77 percent of us make all our trips by car. So if we know that it's healthier to walk, will developing more walkable neighbourhoods help to break the habit and get us walking to the store instead? Researcher Marianne Clark in the Faculty of Physical Education and Recreation set out to investigate the factors that influence the decisions made by key st ... read more
Storm delays deployment of Gulf containment vessel: official|
Polls in quake-hit Haiti set for November
Dozens of children reportedly among China landslide victims
China struggles to find 106 still buried in landslide
Apple hit with lawsuit over iPhone 4 antenna woes
New Multi-Year LTA With EADS Astrium To Power All GEO Satellites
Google News revamped to get more personal
Ball Aerospace Begins Integration Of CrlS Instrument For NPP Weather Satellite
Whiter Clouds Could Mean Wetter Land
Asia in the grip of water crisis: Asian Development Bank
Britain had driest start to year since 1929: forecasters
Deep Thinking On The World's Oceans
China sets sail for the Arctic
Answer To What Ended The Last Ice Age May Be Blowing In The Winds
New Light On Antarctica's Melting Pine Island Glacier
Antarctic ice melt: 10 percent of sea rise
Institutions snap up China AgBank subscriptions
China's AgBank launches world-record IPO
Paraguay dispels gloom with soya bonanza
Maize Prices Driving A Rise In Feed Prices
Romania flood death toll climbs to 24: official
Hurricane Alex churns across northeast Mexico
One dead in strong Mexico quake
Hurricane Alex delays Gulf oil cleanup efforts
Foreign agents in shooting of Rwandan general: S.Africa
G.Bissau army chief installed despite international protest
U.S. military contractors eye Africa
Nigerian leader to promote more foreign investment
Man-Made Global Warming Started With Ancient Hunters
If We Build 'Walkable' Neighborhoods, Will People Walk
Discovery Of 3.6 Million-Year-Old Relative Of 'Lucy'
3.6 million-year-old 'Lucy' relative found
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2010 - SpaceDaily. AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement|