Image caption The study says climate change may drive up to 6.7m Mexicans across the border into the US by 2080

A warming climate could see millions of adult Mexicans migrate to the US as rising temperatures cause a drop in crop yields, according to a study by researchers at Princeton University.

For every 10% of lost crop yields in Mexico, another 2% of Mexicans are likely to leave their country, the study says.

The research draws a clear connection between climate change and immigration - two heavily debated issues in the US.

It says warming may bring between 1.4m and 6.7m Mexicans to the US by 2080.

Many climate experts say human activity is contributing to an increasingly warm planet.

And now a team of researchers led by Michael Oppenheimer says rising temperatures affecting crops through floods, droughts, and stronger storms will induce some workers to relocate.

Farmers migration

"Climate change is expected to cause mass human migration, including immigration across international borders," says the study.

The research, published in the Proceedings of the National Academy of Sciences, said a 10% reduction in crop yields would lead an additional 2% of the population to emigrate.

"It has been well established that farmers do tend to want to migrate when they are not doing so well," Mr Oppenheimer told the Reuters news agency.

The study used census data from 1995 to 2005 as well as statistics on climate data and crop production, which allowed the group to calculate a projected rate of migration.

According to a variety of "warming scenarios", the researchers estimated that by the year 2080, between 1.4 million and 6.7 million adult Mexicans (or 2% to 10% of the current population aged 15-65) would seek to emigrate to the US.

Mr Oppenheimer, a member of the Intergovernmental Panel on Climate Change, said the findings drew attention to "the need to grapple with greenhouse gases".

Experts say these findings are also relevant to other regions around the world, from Africa to Australia - where Mr Oppenheimer's team predicts migration will become a "significant issue".

The study on Mexican migration comes after last month was declared by scientists to be the hottest June on record.

Roughly 6.7 million of the 11 million undocumented immigrants believed to be in the US are from Mexico.

Meanwhile, a new immigration law is set to take effect on 29 July in the US state of Arizona, which will make it a crime to be in the state without immigration papers.