The researchers said farmers pushed into extreme poverty by failing harvests are likely to commit suicide. "It was both shocking and heart breaking to see that thousands of people face such bleak conditions that they are driven to harm themselves," said Tamma Carleton, researcher at UC Berkeley.
The study said temperature increase of just one degree a day during the growing season leads to roughly 65 suicides across India - whenever that day's temperature is above 20 degree Celsius. A temperature rise of five degree Celsius a day has five times that effect, the researchers said.
"But learning that the desperation is economic means that we can do something about this. The right policies could save thousands," Ms Carleton said.
While high temperature and low rainfall during the growing season substantially drive farmers to commit suicide, similar natural events have no effect on farmers during off-season when few crops are grown, hence implicating agriculture as the critical link.
The study, published in the journal Proceedings of the National Academy of Sciences, helps explain India's evolving farmer suicide issue, where suicide rate has nearly doubled since 1980.
The study said global warming - forecast to rise three degree Celsius by 2050 - is already taking a toll on India. More than half of India's working population is employed in rain-dependent agriculture, long known to be sensitive to climate fluctuations such as unpredictable monsoon, heat waves and drought. A third of India's workers already earn below the international poverty line.
Ms Carleton tested the links between climate change, crop yields and suicide by pairing the numbers for India's reported suicides in each of its 32 states between 1967 and 2013, using data from the National Crime Records Bureau, along with statistics on India's crop yields and high-resolution climate data.
To isolate the types of climate shocks that damage crops, Ms Carleton focused on temperature and rainfall during June through September, a critical period for crop productivity that is based on the average arrival and departure dates of summer monsoon.
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