Ancient farmers were responsible for spiking the Earth's temperature by 0.9 degrees Celsius over a period of 8,000 years - almost as much as global warming caused in the past 150 years, a new study has found.
The research suggests that "early agricultural" is as powerful as the whole Industrial Revolution in boosting the global warming.
However, the study led by Feng He, a climate scientist at the University of Wisconsin, Madison found that the net warming caused by early humans was only 0.73 degrees.
This was because of a slight cooling of 0.17 degrees due to more sunlight reflecting from cleared land, 'LiveScience' reported.
The study suggests that early cultures were global warming turtles, slowly raising temperatures by adding greenhouse gases such as carbon dioxide and methane to Earth's atmosphere over thousands of years.
According to the UN's Intergovernmental Panel on Climate Change, post-Industrial Revolution societies are climate change rabbits, with temperatures rising about 0.85 degrees Celsius between 1880 and 2012 in contrast, the report said.
The study adds to an ongoing debate over the influence of pre-industrial humans on Earth's climate.
While it is often said that the year 1850 kicked off the global warming, human activities such as deforestation and agriculture could have shifted the climate earlier.
Researchers estimated past global temperatures with climate models that calculated the effects of land-cover changes such as deforestation and irrigation.
They compared climate models of a human-free Earth to a planet crawling with hunter-gatherers and farmers.
The models suggest that carbon dioxide rose about 40 ppm, to 285 ppm, and methane jumped to 790 ppm, a 345 ppm rise, as early humans chopped down trees and irrigated rice fields.
