More than three quarters of the world's suicides occur in developing countries, yet little is known about the drivers of suicidal behavior in poor populations. I study India, where one fifth of global suicides occur and suicide rates have doubled since 1980. Using nationally comprehensive panel data over 47 y, I demonstrate that fluctuations in climate, particularly temperature, significantly influence suicide rates. For temperatures above 20 • C, a 1 • C increase in a single day's temperature causes ∼70 suicides, on average. This effect occurs only during India's agricultural growing season, when heat also lowers crop yields. I find no evidence that acclimatization, rising incomes, or other unobserved drivers of adaptation are occurring. I estimate that warming over the last 30 y is responsible for 59,300 suicides in India, accounting for 6.8% of the total upward trend. These results deliver large-scale quantitative evidence linking climate and agricultural income to selfharm in a developing country.climate | suicide | agriculture | weather impacts | India E ach year, over 130,000 lives are lost to self-harm in India (1). The causes of these deaths are poorly understood; drivers of suicidal behavior remain disputed across scientific disciplines, and nearly all evidence comes from developed country contexts (2-4). Despite lack of substantiation, public debate in India has centered around one possible cause of rapidly rising suicide rates: increasing variability of agricultural income (5, 6). Drought and heat feature prominently in these claims; climate events are argued to damage crop yields, deepening farmers' debt burdens and inducing some to commit suicide in response. With more than half of India's working population employed in agriculture, one third lying below the international poverty line, and nearly all experiencing rising temperatures due to anthropogenic climate change, these arguments appear plausible. However, the relationship between economic shocks and suicide is controversial (3,4,(7)(8)(9), and, in India, the effect of income-damaging climate variation on suicide rates is unknown. Although the national government has recently announced a $1.3 billion climate-based crop insurance scheme motivated as suicide prevention policy (10), evidence to support such an intervention is lacking. Existing work has found that agricultural yields in India rely heavily on growing season temperature and precipitation (11, 12), but it is unclear to what extent, if any, this sensitivity to climate influences suicide rates. Previous studies of income variability affecting suicide in India are anecdotal (5) or qualitative (13-17), and none attempt to identify and synthesize quantitative relationships between climate, crops, and suicides. To fill this knowledge gap, I use a data set from India's National Crime Records Bureau (NCRB), which contains the universe of reported suicides in the country from 1967 to 2013. I pair these data with information on agricultural crop yields and high-resolution climate data to identi...