A widely reported study that links Indian farmers’ suicides to climate change has come under criticism, with some academics accusing it of misunderstanding data, poor analysis and wrong conclusions

India is in the midst of a farm crisis. (Photo by Sanjeev Rohilla)

Academics in India and the US have taken strong exception to a recent study by Tamma Carleton of the University of California, Berkeley, which links farmers’ suicides in the country to rises in temperature due to climate change.

“Temperature does have an influence on agriculture but it is secondary to water. Ours being a tropical country the crops grown are adapted to high temperatures. However, there will be yield losses due to heat stress primarily in rabi (winter) season,” B. Venkateswarlu, Vice Chancellor of Vasantrao Naik Marathwada Krishi Vidyapeeth in Parbani in eastern Maharashtra, which has seen a spate of these suicides in recent years, told indiaclimatedialogue.net. “The large number of suicides happening in central and south India depend mostly on kharif (summer) season, where drought is a major issue causing crop failures and sometimes total loss.” Fluctuations in rainfall may also be due to climate change.

“Therefore, it is erroneous to draw such a conclusion even though the paper is published in a reputed journal and being quoted widely by the press,” says Venkateswarlu. The study, titled Crop-damaging temperatures increase suicide rates in India, was published in the August 15 issue of Proceedings of the National Academy of Sciences (PNAS) of the US.

It is commonly known that peninsular India is in the rain shadow area of the Western Ghats, so the southwest monsoon doesn’t penetrate much into it. Drought is almost perennial here, so rain plays a bigger role than temperature.

Spurious linkages

Two professors from the Tata Institute of Social Studies (TISS) in Mumbai, T. Jayaraman and Kamal Kumar Murari, and Madhura Swaminathan — daughter of eminent agricultural scientist M.S. Swaminathan — of the Indian Statistical Institute (ISI) in Bengaluru are more pointed in their analysis entitled Misunderstanding data, poor analysis, and wrong conclusions: Spurious linkages between extreme temperatures and farmer suicides.

“We consider these claims to be baseless,” they say. “These claims are a consequence of the uncritical use of data, bad assumptions, flawed analysis and unacceptable neglect of the existing literature on global warming and Indian agriculture as well as farmer suicides.”

“Taking the conclusions of the paper at face value would lead, we strongly believe, to dangerously incorrect policy measures,” the TISS-ISI note says. “Such conclusions also divert from the study of the real challenges that global warming, and extreme temperatures in particular, poses for Indian agriculture.”

The paper, they argue, incorrectly uses suicide data; wrongly identifies extreme temperatures for crop production; wrongly identifies only kharif as the relevant agricultural season in which to consider extreme temperatures, and wrongly identifies the relevant crops.

“As a result, the meaning of the correlation that the author claims to find between extreme temperatures and suicides is unclear,” writers of the critique say. “The manner in which the paper analyses the link between extreme temperatures and crop production is wrong.”

“The signatories to this note have themselves conducted a detailed study of the impact of extreme temperatures on crop production in Karnataka, one among several such studies conducted by other responsible Indian and foreign authors,” says the note. “No such study provides any corroborative evidence for the dramatic conclusions of this paper.”

Nuanced approach

Deepti Singh of Columbia University takes a more nuanced approach. “The issue of farmer suicides in India has garnered a lot of attention in recent years and the data shows that farmer suicides are on the rise,” she told indiaclimatedialogue.net. “These incidences are often attributed to deficit monsoonal rains. However, this study finds rising temperatures as a stronger influence on lowering crop yields and consequently, on related farmer suicides.”

Carleton finds that for temperatures above 20˚C, a mere 1˚C increase leads to an average of 70 suicides in the kharif season, which begins with the summer monsoon.

Singh concurs. “Such days have been increasing and have negatively impacted yields in parts of India. This effect is not something farmers might perceive compared to deficit rains, but many studies have demonstrated the negative effect of temperatures beyond a certain threshold on crop yields.” However, she notes that the study does not account for the fact that the occurrence of high temperature days during the monsoon season will likely coincide with low rainfall days.

Carleton has studied data over 47 years, including suicides recorded by the National Crime Records Bureau (NCRB), which is the authoritative source of information on the spate of incidents of self-harm, particularly in peninsular India.

According to her, “Warming over the last 30 years 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 self-harm in a developing country.”

Heat and lower yields

This impact is only witnessed in the 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,” Carleton says.

According to Dr Singh, rainfall is extremely important for the kharif crops and the study shows that good rainfall could lower suicide rates, but it does not find an effect of drought. “The spatial variance of rainfall at the scale that is affecting farmers is not being captured adequately by our datasets. So, while these deficit rainfall conditions might be driving monsoon failures, the effect is difficult to capture in a statistical model,” she told indiaclimatedialogue.net. “Temperatures, on the other hand, have been rising and there has been an increase in the number of extreme days that are harmful to crops. In addition to the direct physiological effect, warm temperatures are also more conducive to pests and diseases.”

Carleton attributes the increasing fluctuations in agricultural income as the main cause of suicides and cites drought and temperature — both induced by manmade climate change — as being responsible. These lead to a drop in crop yields and an increase in indebtedness, driving some farmers to take the extreme step.

In response to queries from indiaclimatedialogue.net, Carleton said: “I look both at temperature and rainfall. While both temperature and rainfall affect suicide rates, temperature is the dominant climatic variable. In my paper, annual suicides fall with rising rainfall during the growing season, indicating that years of low rain do increase the suicide rate. The paper also highlights the role of rainfall, where years of high rain lower the suicide rate, and with a lagged effect, such that that benefits of rain to crop yields during the growing season can help farmers in future years, perhaps through increasing savings.”

“Suicide is an incredibly complex phenomenon with many contributing factors. I isolate the role of climate in determining suicides from all other possible contributing factors by following the same population within India as it experiences a different climate at different points in time,” she said. “So we can think about observing a population during a hot growing season, in which temperatures get to levels that damage crops.”

Not a deterministic relationship

“It’s important to note that this is not a deterministic relationship between temperature and suicide. You can think about this relationship like the rise in car accidents on rainy days. There are many possible factors causing any individual car accident,” Carleton pointed out. “However, we can measure the elevated risk of an accident caused by a rainy day, on top of these other factors like texting and driver error, by comparing total car accident rates on different days. While the rain increases the risk of accidents in general, any individual car accident is still dependent on the situation and choices made by the driver.”

The NCRB has data from 1967 to 2013, which she compares with data on crop yields and high-resolution climate data to examine the link between climatic shifts and suicide rates. As further evidence, she uses district-level data from 13 states to corroborate her findings.

However, she admits, “It does not guarantee that there are no other factors correlated with both suicide and climate within a state that could confound my estimation. However, the robustness of the effect of growing season temperature on suicide rates across many specifications and subsamples makes such confounding factors extremely unlikely.”

She believes that her study has important lessons both for India, which accounts for a fifth of the globe’s population and where more than half the population is engaged in agriculture, as well as other developing countries. It calls for taking steps to adapt to climate change, of which measures she finds no evidence in the last 47 years, as well as protective measures such as crop insurance.

There are a number of other climatic and non-climatic factors that influence suicide rates that are difficult to evaluate in such a framework, says Singh. “For instance, rainfall extremes, not accounted for in this study, even in an overall good monsoon year, can substantially damage crops. “

Previous studies

Two earlier studies on the causes of suicides in Maharashtra have emphasised the other factors. The first, conducted by TISS on order of the Bombay High Court in 2005, concluded: “Repeated crop failures, inability to meet the rising cost of cultivation, and indebtedness seem to create a situation that forces farmers to commit suicide. However, not all farmers facing these conditions commit suicide. it is only those who seem to have felt that they have exhausted all avenues of securing support have taken their lives.”

The second study was by the Indira Gandhi Institute of Development Research in Mumbai for the Maharashtra government the following year. It also stressed that of late, Maharashtra’s gross value addition from agriculture was relatively greater from fruits, vegetables and sugarcane than from food crops. These accounted for less than 8% of the area under cultivation, but nearly 53% of the gross value. “To sum up, there seems to be a larger socio-economic and agrarian crisis,” the study said.

While farmers might have adapted their day-to-day agricultural practices to warming temperatures, other factors such as market prices are more likely to define their crop choices, says Singh. It is entirely possible that farmers might be growing temperature-sensitive crops in regions where temperature extremes are rapidly on the rise, she points out.

“For instance, in the Marathwada district that has experienced a number of farmer suicides, farmers are growing cotton, which is a temperature-sensitive crop,” says Singh. “However, this study does not differentiate the effect of temperature extremes on different crops.”

Finding fault

Economists in India have pointed to similar flaws in a 2010 paper on Linkages among climate change, crop yields and Mexico–US cross-border migration, also published by PNAS. “There are several problems with the analysis,” an economist told indiaclimatedialogue.net. “The over-emphasis on econometric methods is influencing our knowledge so much. This is the second paper from this reputed journal that we are finding fault with; the earlier paper had similar issues.”

“The farmers’ suicides paper uses panel data models, wherein the spatial and temporal fixed effects are believed to account for variations in the dependent variable (say, suicide rate) caused by all variables other than variables of primary interest (in the present context, climate variables including temperature, precipitation, etc.),” he said. “While this is not incorrect in theory, some economists are not entirely convinced by such strong belief in the black-box specification. Among other things such models may fail to account for crucial idiosyncratic shocks and also miss out several policy induced covariate shocks such as access to credit, etc. As a result, the results may overestimate the role played by climate shocks on farmer suicides.”