Washington, Feb 2 (IANS): When European settlers arrived in the Americas, they killed over 56 million indigenous Americans which led to a change in the global climate, a new study finds.

The settlers killed the indigenous people for more than 100 years in South, Central and North America, causing large swathes of farmland to be abandoned and reforested, researchers at University College London, or UCL, said in the study on Friday.

The increase in trees and vegetation across an area the size of France resulted in a massive decrease in carbon dioxide (CO2) in the atmosphere, according to the study.

Carbon levels changed enough to cool the Earth by 1610, the researchers found.

"CO2 and climate had been relatively stable until this point," UCL Geography Professor Mark Maslin, one of the study's co-authors, told CNN on Friday.

"So, this is the first major change we see in the Earth's greenhouse gases."

Before this study, some scientists had argued the temperature change in the 1600s, called the "Little Ice Age", was caused only by natural forces.

But by combining archaeological evidence, historical data and analysis of carbon found in Antarctic ice, the UCL researchers showed how the reforestation -- directly caused by the Europeans' arrival -- was a key component of the global chill.

"For once, we've been able to balance all the boxes and realise that the only way the 'Little Ice Age' was so intense is because of the genocide of millions of people," Maslin added.

According to Maslin, deaths of indigenous Americans directly contributed to the success of the European economy.

Natural resources and food shipped from the New World helped Europe's population to expand. It also allowed people to stop farming for sustenance and begin working in other industries.