Climate change, crop failure, and suicides in India (Guest post by Tamma Carleton)

[This is a guest post by Tamma Carleton, a Doctoral Fellow at the Global Policy Lab and PhD candidate in the Ag and Resource Econ department here at Berkeley]

Last week, I published a paper in PNAS addressing a topic that has captured the attention of media and policymakers around the world for many years – the rising suicide rate in India. As a dedicated student of G-FEED contributors, I focus on the role of climate in this tragic phenomenon. I find that temperatures during India’s main growing season cause substantial increases in the suicide rate, amounting to around 65 additional deaths if all of India gained a degree day. I show that over 59,000 suicides can be attributed to warming trends across the country since 1980. With a range of different approaches I’ll talk about here, I argue that this effect appears to materialize through an agricultural channel in which crops are damaged, households face economic distress, and some cope by taking their own lives. It’s been a pretty disheartening subject to study for the last couple years, and I’m glad to see the findings out in the world, and now here on G-FEED.

First, a little background on suicides in India. The national suicide rate has approximately doubled since 1980, from around 6 per 100,000 to over 11 per 100,000 (for reference, the rate in the U.S. is about 13 per 100,000). The size of India’s population means this number encompasses many lives – today, about 135,000 are lost to suicide annually. There have been a lot of claims about what contributes to the upward trend, although most focus on increasing risks in agriculture, such as output price volatility, costly hybrid seeds, and crop-damaging climate events like drought and heat (e.g. here, here, and here). While many academic and non-academic sources have discussed the role of the climate, there was no quantitative evidence of a causal effect. I wanted to see if this relationship was in the data, and I wanted to be able to speak to the ongoing public debate by looking at mechanisms, a notoriously thorny aspect of the climate impacts literature.

The first finding in my paper is that while growing season temperatures increase the annual suicide rate, also hurting crops (as the G-FEED authors have shown us many times over), these same temperatures have no effect on suicides outside the growing season. While the results are much less certain for rainfall (I’m stuck with state-by-year suicide data throughout the analysis), a similar pattern emerges there, with higher growing season rainfall appearing to cause reductions in suicide: 

These effects seem pretty large to me. As I said above, a degree day of warming throughout the country during the growing season causes about 65 suicides throughout the year, equivalent to a 3.5% increase in the suicide rate per standard deviation increase in growing season degree days. 

The fact that the crop response functions are mirrored by the suicide response functions is consistent with an agricultural mechanism. However, this isn’t really enough evidence. Like in other areas of climate impacts research, it’s difficult to find exogenous variation that turns on or shuts off the hypothesized mechanism here –  I don’t have an experiment where I randomly let some households’ farm income be unaffected by temperature, as others’ suffer. Therefore, aspects of life that are different in the growing and non-growing seasons could possibly be driving heterogeneous response functions between temperature and suicide.  Because this mechanism is so important to policy, I turn to a couple additional tests.

I first show that there are substantial lagged effects, which are unlikely to occur if non-economic, direct links between the climate and suicidal behavior were taking place (like the psychological channels linking temperature to violence discussed in Sol and Marshall’s work). I also estimate spatial heterogeneity in both the suicide response to temperature, as well as the yield response, and find that the locations where suicides are most sensitive to growing season degree days also tend to be the locations where yields are most sensitive: 

The fact that higher temperatures mean more suicides is troubling as we think about warming unfolding in the next few decades. However, I’m an economist, so I should expect populations to reallocate resources and re-optimize behaviors to adapt to a gradually warming climate, right? Sadly, after throwing at the data all of the main adaptation tests that I’m aware of from the literature, I find no evidence of adaptation, looking both across space (e.g. are places with hotter average climates less sensitive?) and across time (e.g. has the response function flattened over time? What about long differences?):

Keeping in mind that there is no evidence of adaptation, my last calculation is to estimate the total number of deaths that can be attributed to warming trends observed since 1980. Following the method in David, Wolfram and Justin Costa-Roberts’ 2011 article in Science, I find that by end of sample in 2013, over 4,000 suicides per year across the country can be attributed to warming. Integrating from 1980 to today and across all states in India, I estimate that over 59,000 deaths in total can be attributed to warming. With spatially heterogeneous warming trends and population density, these deaths are distributed very differently across space:

While the tools I use are not innovative by any means (thanks to the actual authors of this blog for developing most of them), I think this paper is valuable to our literature for a couple reasons. First, while we talk a lot about integrating our empirical estimates of the mortality effects of climate change into policy-relevant metrics like the SCC, this is a particular type of death I think we should be incredibly concerned about. Suicide indicates extreme distress and hardship, and since we care about welfare, these deaths mean something distinct from the majority of the deaths driving the mortality rate responses that we often study. 

Second, mechanisms really matter. The media response to my paper has been shockingly strong, and everyone wants to talk about the mechanism and what it means for preventative policy. While I have by no means nailed the channel down perfectly here, a focus on testing the agricultural mechanism has made my findings much more tangible for people battling the suicide epidemic on the ground in India. I look forward to trying to find ways to improve the tools at our disposal for identifying mechanisms in this context and in others.

Finally, as climate change progresses, I think we could learn a lot from applying David, Wolfram, and Justin’s method more broadly. While attribution exercises have their own issues (e.g. we can’t, of course, attribute with certainty the entire temperature trend in any location to anthropogenic warming), I think it’s much easier for many people to engage with damages being felt today, as opposed to those likely to play out in the future. 

Are the curious trends in despair and diets related?

There’s a new working paper out by Anne Case and Angus Deaton on one of the most curious (and saddest) trends in America – mortality rates for whites have been rising. There have been various stories about these trends, such as this one that first turned me onto it. It’s clear that the proximate causes are an increase in “deaths of despair,” namely suicides, drugs, and alcohol. It’s also clear that self-reported mental health has been declining in this group. But why?

Any explanation has to account for the fact that the same trends aren’t seen in other racial groups, even though many of them have lower incomes (see figure below from Case and Deaton):

It should also account for the fact that the same trend isn’t seen in other predominantly white countries:

One explanation that seems to have gained most traction is that whites “lost the narrative of their lives.” That is, maybe rising economic inequality and other economic trends have affected all groups, but whites expected more. To me this seems plausible but not really convincing.

Ok, so let me offer another theory. I’ll first say that I think it’s a bit off the wall, but I don’t think I’m going crazy (despite Marshall’s frequent hinting that I am). The idea basically stems from another body of literature that I’ve recently been exploring, mainly because I was interested in allergies. Yeah, allergies. Specifically, a bunch of people I know have sworn that their allergies were fixed by eliminating certain foods, and given that some people in my family have bad seasonal allergies, I decided to look into it.

It turns out that wheat is thought by many to trigger inflammation and allergies. But what’s relevant here is that it’s also thought to affect mental health. More than that, there are actually clinical studies like this one showing that depression increases with gluten intake. There are only 22 subjects in that study, which seems low to me but obviously I don’t do that sort of work. A good summary of scientific and plenty of non-scientific views on the topic can be found in this article. Incredibly, there was even a study in the 1960s showing how hospital admission rates for schizophrenia varied up and down with gluten grain rations during World War 2.

So what’s the connection to the trends in deaths of despair? Well the striking thing to me is that wheat effects are generally only seen in white non-hispanics. Celiac disease, for instance, is much lower in other racial groups. Second, it’s apparently known that celiac has been rising over time, which is thought to indicate increased exposure (of all people) to gluten early in life. And the trends are most apparent in whites, such as seen in the figure below from this paper.

Just to be clear, I realize this is mostly speculation. Not only is this not my area of expertise, but I don’t have any data on the regional trends in gluten or wheat intake in the U.S. to compare to the regional trends in death. I’m not even sure that such data exist. It seems that studies like this one looking at trends in gluten consumption just assume the gluten content of foods is fixed, but it also seems a lot of products now have gluten added to make them rise quicker and better. (Some blame the obsession with whole grain foods, which don't rise as quickly.) If anyone knows of good data on trends in consumption, let me know. It would also be interesting to know if they add less gluten in other countries, where mortality rates haven’t risen.

(As an aside: there’s also a recent study looking at wheat and obesity in cross-section. Apparently country obesity rates are related to wheat availability, but not much else.)

Also to be clear, I still like wheat. Maybe having spent most of my career studying wheat producing systems has made me sympathetic. Or maybe it’s the fact that it has sustained civilization since the dawn of agriculture. But I think it’s possible that we recently have gone overboard in how much is eaten or, more specifically, in how much gluten is added to processed food in this country. And even if there’s only a small chance it’s partly behind the trends of despair (which aren’t just causing mortality, but all sorts of other damage), it’s worth looking into.