This article is part of an ongoing series where experts talk about the link between climate change and mental health.

There’s a strange—and tragic—link between rising temperatures and suicide, as Tamma Carleton, an EPA STAR fellow and PhD student in Agricultural & Resource Economics at UC Berkeley, has found in her research.

Carleton is a visiting scholar at Berkeley’s Climate Impact Lab and uses a variety of tools to study how “climate influences social and economic stability around the globe, with a particular focus on developing countries,” as she told me via email. In this interview, Carleton talks specifically about her research around higher temperatures and increased rates of suicide.

The following interview has been edited for length and clarity.

Thrive Global: Can you talk about your research regarding climate change and mental health?
Tamma Carleton: In my recent article, I study the tragic suicide epidemic in India, where suicide rates have nearly doubled since 1980. There has been much public discussion and debate around the contributing factors leading to rising suicides. Many have argued that increasing risks faced by farmers have caused periods of economic destitution in which some individuals will cope by committing suicide. Often, these claims involve climate events, such as scorching heat waves, drought, or flooding, which damage crops and push many into poverty.

I used records of suicides provided by the Indian National Crime Records Bureau to test the hypothesis that climate change has played a role in elevating the risk of suicide in India. I show that when temperatures rise to levels that damage crops, suicide rates also go up. It appears that crop losses are likely the key culprits linking self-harm to hot temperatures. I calculate that warming due to climate change has already caused over 59,000 suicides over the last 30 years. These are deaths that would not have occurred had the warming we’ve observed in the historical climate record not taken place.

“These are deaths that would not have occurred had the warming we’ve observed in the historical climate record not taken place.”

TG: What’s the most surprising thing you’ve found in your research?
TC: We are often hopeful that as climate change gradually unfolds, people and governments will find ways to adapt to warming temperatures. In India, I tested whether the dramatic changes in social and economic circumstances during the years of my sample—1967 to 2013—had facilitated increased adaptation in the form of lowering the population’s suicide risk at high temperatures. Surprisingly and sadly, I find no evidence that populations within India have been able to successfully adapt to a warming climate. The relationship between temperature and suicide is the same across different populations within India, and at different points in time, suggesting that even as India has gradually warmed while experiencing robust economic growth, people appear no better able to cope with high temperatures. Without substantial investments in adaptive technologies and behaviors, this finding implies that it’s likely we will see a sustained rise in suicide rates as climate change continues to unfold in India.

These findings have not necessarily been found in other contexts, where immediate daily or monthly-level links between temperature and suicide have been uncovered without any evidence of an economic (agricultural) channel. Therefore, as you would expect, this relationship linking climate to mental health is likely very context-dependent, and more research is required, particularly in developing countries, to understand the channels through which the climate-mental health link unfolds.

While it is likely that the key findings from this study are most directly applicable to other developing country contexts, there does exist some evidence that similar links between crop-damaging climate events and suicide operate in Australia, suggesting that this phenomenon may not be limited to lower income countries.

TG: What’s the link between climate change and human behaviors like violence? 
TC: There is an extensive literature linking violent behavior and large-scale civil conflict to climate events. In particular, the relationship between temperature and violence at a range of spatial and temporal scales has been shown to be remarkably robust across countries and time periods [see Burke, Hsiang and Miguel, “Climate and conflict”, in the Annual Review of Economics, and Carleton, Hsiang and Burke, “Conflict in a changing climate”, European Journal of Physics].

There are a few different causal mechanisms that are hypothesized to facilitate these temperature effects (also summarized in the above articles). First, economic productivity may be adversely affected by temperature, and this may make engaging in conflict a relatively more attractive endeavor than standard employment. Second, these economic losses could lead to state-wide resource limitations that constrain the state’s ability to keep peace. Both of these channels are usually discussed in developing country contexts where economic output depends critically on agricultural yields, which in turn are sensitive to temperature shocks.

However, there is also evidence that violent behavior is psychologically or neurologically linked to temperature. In many contexts where violent crime responds to temperature, we see this effect happen immediately – e.g. on a hot day, more murders are likely in U.S. counties (see Ranson, 2014) – such that an economic channel would not have time to manifest. This is bolstered by nascent neurological research suggesting that neurotransmitters are affected by temperature, and control over emotions, and particularly violent and aggressive emotions, is negatively impacted by warmer temperatures. This is consistent with recent work by Patrick Baylis of University of British Columbia, who shows that U.S. Twitter users are more aggressive and exhibit negative emotional states on hot days.

Thus, while the link between many kinds of violence and temperature is clear, the possible channels through which this effect occurs are an active area of research.

TG: What are you hopeful about in your research?
TC: Understanding more about the mechanisms linking climate to social outcomes helps us develop solutions to facilitate adaptation in the future. The fact that the climate-suicide relationship I uncover in India appears to materialize through crop damages provides evidence consistent with policies that seek to reduce suicides by weakening the link between a risky climate and agricultural incomes. While my analysis does not have the data required to make specific policy recommendations regarding suicide prevention in India, the finding that crop losses appear to be the key culprit linking the climate to suicide suggests that there are policies we can pursue that may be able to limit the suffering we see.

For example, policies like crop insurance protect farm incomes from the vagaries of the climate. Access to low-interest loans through well-functioning rural credit markets may also help limit the damage caused by warming temperatures, as farmers can access quality seed without incurring debt burdens that become insurmountable. Other possible adaptive responses could include farm-based solutions to protect yields against warming temperatures, such as crop switching to increase heat tolerance, or investment in irrigation technologies to combat rainfall variability. I hope that future research will help to fill this important gap in our understanding of how we can work to slow the tragic rise in suicide in India.