Contrary to popular opinion that global warming  began with the Industrial Revolution, a new study by University of  Wisconsin-Madison scientists has found that global warming began 5,000 to 8,000  years ago with large-scale agriculture production in Asia and extensive  deforestation in Europe.
 The introduction of rice cultivation and tree  removal caused increases in methane and carbon dioxide according to the research  conducted with supercomputers and climate models.  Steve Vavrus, a  climatologist at the University of Wisconsin, explains the study's conclusion,  "I think that the take-home message is that this hypothesis shows that climates  are extremely sensitive to small variations in greenhouse gases."