'Early farmers began global warming'

Farmers who used ���slash and burn��� methods of clearing forests to grow crops thousands of years ago could have increased carbon dioxide levels enough to change the climate, say researchers.

The scientists believe small populations released carbon emissions as they cleared large tracts of land to produce relatively meagre amounts of food. They were much less efficient than farmers using today���s agricultural practices as there were no constraints on land, the Telegraph reported.

The study conducted by researchers at University of Virginia and University of Maryland-Baltimore County said early farming methods, with around 10 times the amount of land per person than is used today, could have created an impact on the climate despite the small number of people in early civilisations.