As more of the greenhouse gas carbon dioxide enters the atmosphere, leading to climate change, crops might carry fewer nutrients, like zinc and iron. Stanford researchers explored this trend and regions most likely to be hurt by it.
As the climate changes, where plants grow best is predicted to shift. Crops that once thrived as a staple in one region may no longer be plentiful enough to feed a community that formerly depended on it. Beyond where plants grow, there’s also the issue of how they grow. Evidence suggests that plants grown in the presence of high carbon dioxide levels aren’t as nutritious.
“Zinc is critical for the immune system and zinc deficiency makes pneumonia, diarrheal illness, malaria more difficult for the body to combat,” said Eran Bendavid, associate professor of medicine. “Iron deficiency has all sorts of manifestations, from lethargy and feeling ill to broader effects, like worse performance in school.”
David Lobell, professor of Earth system science in the School of Earth, Energy & Environmental Sciences, has been studying the relationship between climate change and crops. He was drawn to the relationship between C02 and crop nutrition because his work pairs findings from scientific models with concrete observations.
“Any time you’re looking at data, you need observations that correspond to the conditions you’re trying to understand. But you have to be creative to find data sets that allow for this kind of validation,” Lobell said.
The researchers estimated how many additional years of healthy life would be lost from 2015 to 2050 due to carbon dioxide-related declines in zinc and iron in crops. This data represents the base case scenario, where carbon dioxide levels climb relatively unabetted. These predictions start at 2015 but health disparities between the regions already existed: at that time, the African Region was losing approximately four times as many healthy years due to these nutrient insufficiencies as the European Region. (Image credit: Yvonne Tang)
Last year, Lobell, Bendavid and Stanford collaborators including management science and engineering graduate student Christopher Weyant, published a paper in which they projected how crop nutrition – zinc and iron levels – will respond to climate change in the coming decades and what that might mean for human health. They looked at two different scenarios, one a base case scenario in which carbon dioxide levels climb relatively unabetted, resulting in a nearly 40 percent increase in carbon dioxide concentrations by 2050. In the other, the group assumed global temperatures would remain within 2 degrees Celsius of pre-industrial levels, as proposed by the Paris Agreement.
For each scenario, they calculated how many years of healthy life people around the world would lose due to illness, disability or death as a result of less iron and zinc in their diet. In the base case scenario, they also explored how different health care interventions, including zinc or iron supplementation, and disease control programs for pneumonia, diarrhea and malaria could help.
The researchers estimated total years of healthy life lost from 2015 to 2050 due to carbon-dioxide-related zinc and iron deficiencies, with different interventions. The researchers’ predictions showed that keeping to the Paris Agreement goals and reducing greenhouse gas emissions results in far better health outcomes than other solutions, such as supplementing nutrients. (Image credit: Yvonne Tang)
They projected that, by far, the most effective way to reduce the consequences of this carbon dioxide-induced disease burden was to limit the amount of carbon dioxide in the atmosphere. In their model, sticking to Paris Agreement goals avoided 48.2 percent of the healthy years lost to carbon dioxide-induced nutritional diseases. In contrast, providing health care interventions only reduced years of healthy life lost by 26.6 percent.
As with other research on the impact of climate change, these nutritional deficiencies are more likely to affect the poorest people first and most severely. But Lobell cautions against assuming it is a problem happening somewhere else.
“Even in a world that is getting more and more food secure, malnutrition would be among the biggest – if not the biggest – health effects of climate change,” Lobell said.
Lobell is now studying what large and small farms are currently doing to combat climate change and the effectiveness of those efforts. One aspect of this work is his lab’s analysis of high-resolution images from satellites to estimate crop yields from space.
The way we treat the planet has direct consequences on human health. This series of stories explores some of those consequences and what we can do to lessen the risks.
In warmer temperatures suicide rates increase, leading to concerns about an uptick in suicides as the globe continues to warm. But researchers offer some hope if greenhouse gases get under control.
As global temperatures rise, climate change’s impacts on mental health are becoming increasingly evident. Recent research has linked elevated temperatures to an increase in violence, stress and decreased cognitive function leading to impacts such as reduced test scores, lowered worker productivity and impaired decision-making.
Adding to the concern, a Stanford study led by economist Marshall Burke also finds a link between increased temperatures and suicide rates. The research, published in Nature Climate Change, concluded that up to 21,000 additional suicides will occur by 2050 within the United States and Mexico if unmitigated climate change continues to warm the Earth at the current projected rates.
Suicide is one of the top 10 causes of death in the United States. Unlike other leading causes – which include heart disease, cancer, homicide and unintentional injury – suicide rates have increased rather than fallen over time. And, while there has been a noticeable trend of rising suicide rates in warmer months, up to this point it has been difficult to attribute these changes to temperature, as other factors like day length and social patterns also vary.
Burke and team overcame these obstacles by assembling and examining decades worth of temperature and suicide data across thousands of U.S. counties and Mexican municipalities. To complement the data, they also scanned over half a billion Twitter updates or tweets and looked for language signaling a negative state of mind.
They found that hotter than average temperatures increase both suicide rates and the use of depressive language on Twitter. They also concluded that socioeconomic status had little to no impact, meaning wealth does not help insulate populations from suicide risk.
“One claim you often hear is that it’s the socioeconomically disadvantaged that are going to be affected by climate change. Our results suggest that at least in the case of mental health, impacts are going to cut across the income distribution and could affect any of us,” Burke said.
He and his team then used global climate model projections to predict how future temperatures could affect suicide rates. They found climate change could increase suicide rates by 1.4 percent in the United States and 2.3 percent in Mexico by 2050.Excess suicides by 2050 caused by warmer temperatures if greenhouse gas emissions stabilize consistent with Paris Agreement goals (move the slider to the right), or if emissions continue unabated (move the slider to the left). (Image credit: Sam Heft-Neal)
Given this increasing overall health burden, the researchers assert even small changes in suicide rates due to climate change could result in large human costs. Also, if similar relationships hold true in other countries, where suicide rates are sometimes even higher than in the U.S. and Mexico, changes in the associated global health burden may be much larger.
“Clearly, climate is not the only factor affecting mental health, and many approaches to addressing the growing mental health challenge will have nothing to do with climate,” Burke said. “But we find clear evidence that a warming climate is going to exacerbate the burden of poor mental health and ignoring this evidence is going to cause unnecessary harm and anguish for a lot of individuals and families inside our country and out.”
The way we treat the planet has direct consequences on human health. This series of stories explores some of those consequences and what we can do to lessen the risks.
Our Report draws attention to a complex but understudied issue: How will climate warming alter losses of major food crops to insect pests? Because empirical evidence on plant-insect-climate interactions is scarce and geographically localized, we developed a physiologically based model that incorporates strong and well-established effects of temperature on metabolic rates and on population growth rates. We acknowledged that other factors are involved, but the ones we analyzed are general, robust, and global (1–3).
Parmesan and colleagues argue that our model is overly simplistic and that any general model is premature. They are concerned that our model does not incorporate admittedly idiosyncratic and geographically localized aspects of plant-insect interactions. Some local effects, such as evidence that warmer winters will harm some insects but not others, were in fact evaluated in our sensitivity analyses and shown to be minor (see the Report's Supplementary Materials). Other phenomena, such as plant defenses that benefit some insects and threaten others, are relevant but are neither global nor directional. Furthermore, because Parmesan et al. present no evidence that such idiosyncratic and localized interactions will outweigh the cardinal and universally strong impacts of temperature on populations and on metabolic rates (1–3), their conclusion is subjective.
We agree with Parmesan and colleagues that the question of future crop losses is important and needs further study, that targeted experimental data are needed (as we wrote in our Report), and that our estimates are likely to be conservative (as we concluded, but for reasons different from theirs). However, we strongly disagree with their recommendation to give research priority to gathering localized experimental data. That strategy will only induce a substantial time lag before future crop losses can be addressed.
We draw a lesson from models projecting future climates. Those models lack the “complexity and idiosyncratic nature” of many climate processes, but by building from a few robust principles, they successfully capture the essence of climate patterns and trends (4). Similarly, we hold that the most expeditious and effective way to anticipate crop losses is to develop well-evidenced ecological models and use them to help guide targeted experimental approaches, which can subsequently guide revised ecological models. Experiments and models should be complementary, not sequential.
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Curtis A. Deutsch, Joshua J. Tewksbury, Michelle Tigchelaar, David S. Battisti, Scott C. Merrill, Raymond B. Huey
Dr. Noah Diffenbaugh is the Kara J Foundation Professor and Kimmelman Family Senior Fellow at Stanford University. He studies the climate system, including the processes by which climate change could impact agriculture, water resources, and human health. Dr. Diffenbaugh is currently Editor-in-Chief of the peer-review journal Geophysical Research Letters. He has served as a Lead Author for Working Group II of the Intergovernmental Panel on Climate Change (IPCC), and has provided testimony and scientific expertise to the White House, the Governor of California, and U.S. Congressional offices. Dr. Diffenbaugh is a recipient of the James R. Holton Award from the American Geophysical Union, a CAREER award from the National Science Foundation, and a Terman Fellowship from Stanford University. He has also been recognized as a Kavli Fellow by the U.S. National Academy of Sciences, and as a Google Science Communication Fellow.
Marshall Burke, assitant professor of Earth system science and deptuy director at the Center on Food Security and the Enviroment shares his insights on how climate change is already impacting human behavior and what interventions are cost effective when it comes to combating the global change in climate.
Walter Falcon, the Helen Farnsworth Professor of International Agricultural Policy in Economics (emeritus), writes from an unusual perspective. During the academic year he serves as a senior fellow with the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment. He spends the summers on his family farm near Marion, Iowa. He returns to campus each year with reflections on the challenges and rewards of faming life in his "Almanac Report." Falcon is former deputy director of the Center on Food Security and the Environment.
These field notes constitute my seventh summer report from our Iowa farm. As readers of prior postings may remember, my wife and I own a medium-sized farm in east-central Iowa that produces corn, soybeans, and beef from a cow-calf herd. We are fourth-generation custodians of these acres – a long-term family relationship that is typical for many Iowa farms. The atypical dimension of our operation is that I am also a Professor at Stanford University, where I have done research and taught courses on the world food economy for more than 40 years. This contrast in surroundings could not be more stark, which I hope generates field notes of interest to friends at both locations.
The title for this year’s edition is probably redundant. Farmers throughout the world ALWAYS talk about bad weather, low prices, and inept governments. That combination has certainly been front and center this year. The 8 a.m. gathering of farmers at our old Waubeek “restaurant” on the Wapsipinicon River continues to produce interchanges on the latest farm happenings, usually about who or what is to blame for distressed rural conditions.
Trump trade-wars, with farmers as casualties came up frequently in the conversations. There also seemed to be less banter this year and fewer new pick-up trucks.
There has been justifiable concern about the weather, since the 2018 crop year has been strange, even for Iowa. The year began very early, with corn tasseling by Independence Day – completely destroying the old maxim of knee-high by the Fourth of July. Many days of intense heat then occurred during the kernel-filling stage, prompting concerns about low test-weights for the projected harvest. Nevertheless, in late July, both corn and soybeans held prospects for record crops.
Then in August the rain gods became agitated. The local newspaper ran the headline “Rain, Rain, Rain – Heat, Humidity, Tornadoes & Floods.” We received 12 inches of rain in 10 days. Nearby creeks and rivers overflowed; soybeans got driven into the mud from the hard rains and the accompanying high winds; and we dodged a nearby tornado spinning away about four miles from us.
Wet conditions caused white mold and spurred “sudden death syndrome” in some soybean fields – the latter caused by a soil fungus that seems to thrive in damp conditions. Corn ears that had not “fallen” (going from their upright-pointed position on the stalk to the downward position that occurs with maturity) began to collect moisture, creating mildew and ear rot inside the husk. Corn having more than 4 percent damage is very difficult to sell without large price discounts, or to use as cattle feed.
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Credit: D. Hogan, example of damaged ear from our farm.
Farmers are also growing increasingly concerned about the added propane costs that will be incurred if corn must be dried before it can be sold. They worry as well that elevators and other shipping points will be “full” because of trade disruptions. Crops that had looked so promising on August 1looked more dubious on September 15.
There is a tendency always to generalize nationally from local conditions, but the prevailing neighborhood view is that the USDA has overestimated the harvest. These conditions have also created considerable discussion about climate change and extreme weather events. For farmers, the concerns are not about climate science, but are much more about risk, farm profitability, and upcoming conversations with bankers.
The weather uncertainty has been compounded by price and trade issues. Soybean prices plunged to a nine-year low, and in mid-September cash prices in rural Iowa markets were about $7.25 per bushel. That level was only about 70 percent of prices in 2013 – even without adjusting for inflation. The soybean supply chain is congested with large stocks in elevators, and uncertainty about the direction of flows is affecting cash prices. Will Midwestern beans go to Pacific ports for shipment to China, as has been the case in recent years, or will they go to Atlantic and Gulf ports for shipment to Europe, as Brazil and the U.S. (partially) exchange customers because of trade disruptions?
At the other end of the crop-price spectrum, hay and straw markets have gone crazy in the opposite direction. Supplies of both are in short supply, largely because of drought in the southern plains and floods in the northern Midwest.
Prices of hay for our cowherd were more than double that of last year, and we also paid dearly – $75 per 3’ x 3’ square bale – for straw that originated in North Dakota! More famers will bale corn stalks for use as bedding this year, but for reasons of nutrients, tilth, and erosion, we are reluctant to remove corn residues from our fields.
The livestock sector also poses a murky outlook for (the typically large) farmers who specialize in raising pigs and/or feeding cattle. Though helped by low feed prices, both the pork and beef sectors are plagued with large numbers of animals on feed, with uncertain exports to China, Mexico, and Europe, and with high prices for replacement animals.
Given the smallness of our cowherd – for us, a cheaper sport than golf – the economic consequences are not overly severe. Even so, we are looking at a great calf crop, the prize of which is “my” shorthorn steer calf shown below. “My” is used advisedly, since my wife would prefer that our herd be Angus, whereas my family’s tradition was with Shorthorns. I was in special trouble, therefore, when, during my Stanford absence, my wife and a neighbor had to pull this particular calf in the middle of the night in a driving rainstorm. As for the herd more generally, we have compromised. Half are Shorthorn and half are Angus, and this year my wife won the tiebreaker – our herd bull is mostly Angus. He is massive, fitting his name “Samson,” and he is both a pet and a pest. He is trained to lead, likes people, knows his name, and sometimes behaves like a kitten. Unfortunately, his well-intentioned shoulder nudges can send one sailing.
Credit: L. Harney: “Hogie” at two months.
Credit: L. Harney, “Hogie” at two months.
The implications of commodity prices on land prices are still uncertain as very little cropland is being offered for sale. But negotiations on cash rents are much more contentious this year. There is quite clear evidence that cash rents, many of which were in the $275-$300 per acre range only a couple of years ago, have come down by 20 percent.
This somewhat dismal rural outlook sets the scene for the upcoming midterm elections. Iowa voted for Trump in 2016, where he ran very strongly in rural areas. As an “outside-insider” (especially from California!) it has been especially challenging for me to read the current political attitudes of farmers. They do not talk politics very openly, so I first looked at what was happening at the Iowa State Fair.
Even without the obvious political overlay, the fair was spectacular. It attracted more than a million visitors – remarkable given that Iowa has only 3.1 million people in total. The traditional cow, sculpted in 600 pounds of butter, stood alongside a butter version of a “1919 Waterloo Boy,” a forerunner to John Deere tractors.
Then there was also the new culinary treat – pork belly with brown sugar on a stick. This specialty was complemented by a demonstration of foot-stomping wine making. Not surprisingly, I drew MUCH anti-California ire when I suggested that this process might actually improve the quality of Iowa wine. And of course there was superbull (3,030 pounds) and superboar (1,165 pounds)!
Credit: Iowa State Fair, butter sculpture of Jersey cow and1919 tractor.
What was most notable, at least to me, was the fair’s political overtone – “corn dogs with a side of politics” noted one local pundit. There was lots of campaigning for state-level offices, and also for the races for the U.S. House of Representatives. At the national level, one would have thought it was 2020. Presidential hopefuls showed up in large numbers. One candidate known by almost no one, John Delaney, had already visited all 99 Iowa counties – a “full Grassley,” named after Iowa’s long-term Senator who has made 38 annual visits to all 99 counties an integral part of his political strategy.
The question that I most hear from my liberal California friends concerns buyer’s remorse. Their assumption is that with tariffs, trade, turmoil, and Trump, farmers must be up in arms and ready to change their political allegiance. My conjecture is that many are not changing – at least not yet – and that the reasons are complicated.
Iowa’s population is now more than 90 percent white, with the farmer percentage even higher. Many farmers, and especially rural women, do not care for Trump or his shaky moral compass; however they are not resonating to Democratic minority messaging either. They like tax cuts, and especially the prospects of E15 ethanol that the president and secretary of agriculture have been dangling in front of them.
Soybean farmers might seem to have the most to complain about as a result of the Chinese imposition of retaliatory tariffs on U.S. soybeans as part of the ongoing trade war. Soybean exports to China through July 2018 were down more that 50 percent as compared to last year. On the other hand, the value of total soybean exports was off by only 8 percent as a consequence of substituting customers among U. S., Brazilian, and other exporters.
I also sense two other related points. First, farmers seem to be assuming (hoping?) that the trade war will be a matter of months not years. Second, many have not yet “priced” (hedged or sold for forward delivery) much of the current year’s soybean crop. In that sense, the tariff/trade impacts have yet to hit home. When they do, political views may change. Interestingly, the bulk of the soybean harvest will occur just a month before the mid-term elections.
Government policy is also at work. While all of the key farm organizations are on record as preferring trade to subsidies, farmers will certainly cash government checks! Under a supplemental program announced by the president (some would say cynically as an election-year “sweetener” for his wrong-headed tariff policy), soybean farmers with yields of 50 bushels per acre will receive a special bonus of about $40 per acre.
Finally, crop insurance serves as a safety net. More than 90 percent of Iowa soybean farmers purchase 80 percent, revenue-guaranteed insurance. This insurance contains key price and yield details, but basically, farmers are compensated for any gross-revenue losses – whether caused by yields or prices – of greater than 20 percent as compared to what they received in 2017.
Whatever one may think about farmer political preferences, the economics of their changing that support is much more complicated than first meets the eye. My conclusion is that Iowa will continue to be a fierce battleground state, and that neither Republicans nor Democrats can take Iowa for granted in either 2018 or 2020.
Iowa is not exactly a major tourist destination. With a few exceptions, like the state fair and the bike ride across Iowa (RAGBRAI) where 20,000 bicyclists (willingly!) ride 450 miles in the summer heat from the Missouri River on the west to the Mississippi River on the east, the common view is that not much happens here.
When my wife and I were growing up, “tourism” meant going for short Sunday drives. Mostly these trips were for the purpose of our fathers comparing the straightness of neighbors’ cornrows. And there were always “Sauerkraut Days” in the town of Lisbon, “Pickle Days” in Walker, plus all of the church-sponsored ice cream socials and dinners.
Then as now, however, Iowa is dotted with interesting historical communities, especially the Amish who settled in Iowa during the last half of the 19thcentury. We have restarted the short-drive tradition, and one of the more interesting visits was to Hopkington, an Amish community just to our north. The devout members of the community do not believe in motors or electricity, and the local scenes are very bucolic: large white houses, not electrified, for their typically large families; horse-drawn farming implements and horse-drawn buggies tied up in neat rows at the church; women in long skirts and bonnets and men with bib-overalls and wide brimmed hats; and wonderful baked goods, cheeses, quilts, and other specialties for sale at roadside stands.
Credit: R. Naylor, Amish buggy and roofers at work.
Horse sales are big events in these communities, with both draft and driving horses featured at auction. Truth in advertising seems to be the order of the day – though I confess some of the descriptions had me thinking of Washington, D. C. For example, an eight-year old draft horse –“pulls hard from either the right or left side”, and a three-year old gelding – “leads real well, but needs more time on the buggy.”
The Amish are struggling with the 21stcentury. Finding enough farmland, in keeping with their tradition of providing all sons with space to farm, is causing some of these communities to break apart. The correct type of schooling is also an issue. And adapting religious norms raises both questions and eyebrows.
It is interesting that a high percentage of all of the roofing of barns and other farm buildings in the entire region is done by Amish men. But how do they get to job sites? If it is too far to drive their horses, they now deem it acceptable to ride in autos with others, so long as they do not drive. A friend of ours is essentially the “Uber-driver” for the Amish roofers of Hopkington. It is interesting, in Iowa and the entire world, what happens when economics and religion clash.
For someone whose day job has been teaching risk analysis and the world food economy, being in Iowa during the summer of 2018 was like living in a 24/7 laboratory. I hope that this experience has given me both the inspiration and ammunition to keep ahead of a fresh batch of bright Stanford students, many of whom have never been on a farm. I will soon know – classes begin this week.
Experts gathered to discuss the linkages between climate change and health at a Stanford-led event at the Global Climate Action Summit.
When it comes to food security, health and poverty, the impacts of climate change already are evident. That’s the message FSE Fellows David Lobell and Marshall Burke delivered last week at Global Climate Action Summit events held by Stanford in San Francisco. Attendees from across the globe gathered at the summit aimed to mobilize commitments and action from local governments, corporations and NGO’s to mitigate climate change and reach the goals of the Paris Agreement.
Lobell and Burke – a professor and assistant professor (respectively) in Earth system science in Stanford’s School of Earth, Energy & Environmental Sciences participated in the Stanford Woods Institute for the Environment sponsored panel on Sept. 14 “The 2009 EPA ENDANGERMENT FINDING: EVEN STRONGER EVIDENCE in 2018.” Moderated by Stanford Woods Institute Director Chris Field, the panel examined how new research bolsters the original report’s findings that greenhouse gases pose a threat to human health and welfare.
Crop responses to climate warming suggest that yields will decrease as growing-season temperatures increase. Deutsch et al. show that this effect may be exacerbated by insect pests (see the Perspective by Riegler). Insects already consume 5 to 20% of major grain crops. The authors' models show that for the three most important grain crops—wheat, rice, and maize—yield lost to insects will increase by 10 to 25% per degree Celsius of warming, hitting hardest in the temperate zone. These findings provide an estimate of further potential climate impacts on global food supply and a benchmark for future regional and field-specific studies of crop-pest-climate interactions.
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Curtis A. Deutsch, Joshua J. Tewksbury, Michelle Tigchelaar, David S. Battisti, Scott C. Merrill, Raymond B. Huey
Solar radiation management is increasingly considered to be an option for managing global temperatures1,2, yet the economic effects of ameliorating climatic changes by scattering sunlight back to space remain largely unknown3. Although solar radiation management may increase crop yields by reducing heat stress4, the effects of concomitant changes in available sunlight have never been empirically estimated. Here we use the volcanic eruptions that inspired modern solar radiation management proposals as natural experiments to provide the first estimates, to our knowledge, of how the stratospheric sulfate aerosols created by the eruptions of El Chichón and Mount Pinatubo altered the quantity and quality of global sunlight, and how these changes in sunlight affected global crop yields. We find that the sunlight-mediated effect of stratospheric sulfate aerosols on yields is negative for both C4 (maize) and C3 (soy, rice and wheat) crops. Applying our yield model to a solar radiation management scenario based on stratospheric sulfate aerosols, we find that projected mid-twenty-first century damages due to scattering sunlight caused by solar radiation management are roughly equal in magnitude to benefits from cooling. This suggests that solar radiation management—if deployed using stratospheric sulfate aerosols similar to those emitted by the volcanic eruptions it seeks to mimic—would, on net, attenuate little of the global agricultural damage from climate change. Our approach could be extended to study the effects of solar radiation management on other global systems, such as human health or ecosystem function.
By comparing historical temperature and suicide data, researchers found a strong correlation between warm weather and increased suicides. They estimate climate change could lead to suicide rate increases across the U.S. and Mexico.
Suicide rates are likely to rise as the earth warms, according to new research published July 23 in Nature Climate Change. The study, led by Stanford economist Marshall Burke, finds that projected temperature increases through 2050 could lead to an additional 21,000 suicides in the United States and Mexico.
“When talking about climate change, it’s often easy to think in abstractions. But the thousands of additional suicides that are likely to occur as a result of unmitigated climate change are not just a number, they represent tragic losses for families across the country,” said Burke, assistant professor of Earth system science in the School of Earth, Energy & Environmental Sciences at Stanford.
Researchers have recognized for centuries that suicides tend to peak during warmer months. But, many factors beyond temperature also vary seasonally – such as unemployment rates or the amount of daylight – and up to this point it has been difficult to disentangle the role of temperature from other risk factors.
“Suicide is one of the leading causes of death globally, and suicide rates in the U.S. have risen dramatically over the last 15 years. So better understanding the causes of suicide is a public health priority,” Burke said.
Heat and suicide
To tease out the role of temperature from other factors, the researchers compared historical temperature and suicide data across thousands of U.S. counties and Mexican municipalities over several decades. The team also analyzed the language in over half a billion Twitter updates or tweets to further determine whether hotter temperatures affect mental well-being. They analyzed, for example, whether tweets contain language such as “lonely,” “trapped” or “suicidal” more often during hot spells.
The researchers found strong evidence that hotter weather increases both suicide rates and the use of depressive language on social media.
“Surprisingly, these effects differ very little based on how rich populations are or if they are used to warm weather,” Burke said.
For example, the effects in Texas are some of the highest in the country. Suicide rates have not declined over recent decades, even with the introduction and wide adaptation of air conditioning. If anything, the researchers say, the effect has grown stronger over time.
Effect of climate change
To understand how future climate change might affect suicide rates, the team used projections from global climate models. They calculate that temperature increases by 2050 could increase suicide rates by 1.4 percent in the U.S. and 2.3 percent in Mexico. These effects are roughly as large in size as the influence of economic recessions (which increase the rate) or suicide prevention programs and gun restriction laws (which decrease the rate).
Effects of historical temperature changes on suicide rates are shown for the U.S. and Mexico. (Image credit: Marshall Burke)
“We’ve been studying the effects of warming on conflict and violence for years, finding that people fight more when it’s hot. Now we see that in addition to hurting others, some individuals hurt themselves. It appears that heat profoundly affects the human mind and how we decide to inflict harm,” said Solomon Hsiang, study co-author and associate professor at the University of California, Berkeley.
The authors stress that rising temperature and climate change should not be viewed as direct motivations for suicide. Instead, they point out that temperature and climate may increase the risk of suicide by affecting the likelihood that an individual situation leads to an attempt at self-harm.
“Hotter temperatures are clearly not the only, nor the most important, risk factor for suicide,” Burke emphasized. “But our findings suggest that warming can have a surprisingly large impact on suicide risk, and this matters for both our understanding of mental health as well as for what we should expect as temperatures continue to warm.”
Credit: L. Harney: “Hogie” at two months.
Effects of historical temperature changes on suicide rates are shown for the U.S. and Mexico. (Image credit: Marshall Burke)