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SANTA FE, N.M. — People started influencing their home planet’s climate millennia before the industrial revolution’s fossil fuel–burning machines began spewing carbon dioxide and other heat-trapping gases into the atmosphere, a new study suggests.
Clearing land — first to hunt and gather, and then to farm — removed trees that otherwise would have soaked up carbon dioxide. The new work suggests that humans working the land put nearly 350 billion metric tons of carbon — many times other estimates — into the atmosphere by the year 1850. (For comparison, between 1850 and 2000 people added 440 billion tons of carbon, mostly from burning fossil fuels — surpassing in a century and a half what had previously taken humankind eight millennia.)