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To: Maurice Winn who wrote (61780)	4/12/2005 4:46:12 PM
From: Snowshoe	Read Replies (1) \| Respond to of 74559

>>we have almost avoided flipping into another ice age by producing all that CO2... A bit more CO2 and we should be home free!<< Yes, but if we overshoot we'll be cooked. This March 2005 Scientific American article suggests that humans have already been changing the climate for thousands of years... How Did Humans First Alter Global Climate? A bold new hypothesis suggests that our ancestors' farming practices kicked off global warming thousands of years before we started burning coal and driving cars By William F. Ruddiman The scientific consensus that human actions first began to have a warming effect on the earth's climate within the past century has become part of the public perception as well. With the advent of coal-burning factories and power plants, industrial societies began releasing carbon dioxide (CO2) and other greenhouse gases into the air. Later, motor vehicles added to such emissions. In this scenario, those of us who have lived during the industrial era are responsible not only for the gas buildup in the atmosphere but also for at least part of the accompanying global warming trend. Now, though, it seems our ancient agrarian ancestors may have begun adding these gases to the atmosphere many millennia ago, thereby altering the earth's climate long before anyone thought. New evidence suggests that concentrations of CO2 started rising about 8,000 years ago, even though natural trends indicate they should have been dropping. Some 3,000 years later the same thing happened to methane, another heat-trapping gas. The consequences of these surprising rises have been profound. Without them, current temperatures in northern parts of North America and Europe would be cooler by three to four degrees Celsius--enough to make agriculture difficult. In addition, an incipient ice age--marked by the appearance of small ice caps--would probably have begun several thousand years ago in parts of northeastern Canada. Instead the earth's climate has remained relatively warm and stable in recent millennia. ... (continued at Scientific American Digital for subscribers) sciam.com