Photographer: Jean-Sebastien Evrard/AFP via Getty Images

Blame Global Warming for Your Bad Attitude

Climate change is making us angry. It may also cause more assaults, murders, and even poor math grades for your kids.

It doesn’t take a PhD to see that climate affects our lives. Anyone who lives far enough from the equator can tell just by opening the closet.

It takes a lot of scientists, however, to reveal how climate affects us—particularly as our climate changes. Sure, there’s prolonged heat and drought in some places, persistent floods and storms in others—all the ways we’ve learned to see global warming (though some still reject the science). But an exhaustive review of almost 200 different studies reveals not only the extent of those predictable changes but also how we humans are reacting to climatic wallops. The results are troubling. 

Richard Moss, senior scientist at Pacific Northwest National Laboratory’s Joint Global Change Research Institute, calls the study essential to making clear the everyday price of climate change. Moss, who led the climate division of the U.S. Global Change Research Program and contributes to the National Climate Assessment, said “it’s always been a challenge in some of our national conversations.”

Thinkers at least as old as Aristotle asked how climates shape societies, the authors of the new analysis note. The trouble with answering that question in a thorough manner is that scientists would have to measure pretty much everything all the time. This new super study, published Thursday in the journal Science, shows that scientists have become extremely clever at drawing conclusions by combining data they have with novel statistical approaches. 

In their analysis, researchers at the University of California at Berkeley deployed these tools to assess the societal consequences of climate change. They lend support to earlier conclusions on how it’s slowing global economic growth (by 0.25 percentage points every year) and has raised the risk of conflict in Africa (by 11 percent since 1980). But there are other, less predictable impacts as well.  

1. What an “adaptation gap” looks like

One thing science has brought to agriculture is a more precise understanding of how crops perform at specific temperatures and at vital stages of their growth cycles. If any country can insulate itself from the shocks of warming, it’s probably the U.S. Yet even among American farmers, studies have concluded that plenty of adaptation are needed, particularly in the South. The chart below left shows that the South and Central U.S. have a greater sensitivity to higher temperature than in the North—possibly in part a function of crop insurance distorting incentives to adapt. The chart on the right projects corn behaving somewhat similarly in both slow and fast warming scenarios. 

“It's a big mystery,” said Solomon Hsiang, who along with Tamma Carleton authored the new paper. “In some locations, we see really high levels of adaptation, and in other places we see nothing.”

Carleton maize
SOURCE: Tamma Carleton and Solomon Hsiang; journal Science

2. Heat disrupts human reproduction

Higher temperatures affect human sexual behavior, the researchers found. Birth rates drop nine months after heat spells, bouncing back reliably nine months after the heat breaks. In this case, the adaptation is a delay, rather than a decline, in regular patterns. 

Carleton birth delays

A decline in births nine months after hot spells tends to be followed by a rebounding rise in average births. 

SOURCE: Tamma Carleton and Solomon Hsiang; journal Science

3. More storms may mean more infant mortality

Cyclone damage is bad enough, leaving poor communities broken and without resources to recover. In the Philippines, data suggest that in the months after a major storm, female infant mortality leaps. In the post-storm dislocation, when the local economy is thrashed and everything and everyone needs help or attention, infant girls may receive among the least of it. The infant-female mortality rate is twice as high in families where there is an older sibling, and twice as high as that in families where the older sibling is male, Hsiang said. 

The mortality rate of female infants rises dramatically in the months after the Philippines faces a tropical cyclone.
The mortality rate of female infants rises dramatically in the months after the Philippines faces a tropical cyclone.
SOURCE: Tamma Carleton and Solomon Hsiang; journal Science

4. People secretly hate heat

It’s easy to imagine that warmer weather might make people happier. After all, summer brings beaches and bikes, and hiking and barbecues.

That may not be the case, according to a 2014 paper [pdf] that analyzed a billion Twitter posts and scored them across a happiness index. Above 70 degrees Fahrenheit or so, the mood of Twitter users changed, evidenced in part by an uptick in profanity. The difference in user happiness scores during 60F to 70F weather and 80F to 90F weather was similar to the difference in people’s moods on Sundays vs. Mondays.

Carleton Profanity

A 2015 analysis of a billion tweets concluded that heat makes people upset, with a detectable uptick in profanity as temperature rose above about 70 degrees Fahrenheit.

SOURCE: Tamma Carleton and Solomon Hsiang; journal Science

It may sound frivolous, but the Twitter study opens up a critical question for projections of economic damages from climate change. If climate-economic models assume that warmer temperatures bring better living, but it turns out that they now bring frustration and short-tempers, current estimates of future economic damages may be low by a considerable margin. 

5. Heat and violence may be linked

A 2014 study in the Journal of Environmental Economics & Management drew attention by comparing increases in violent crime in the U.S. to the rate of global warming and concluding that “temperature has a strong positive effect on criminal behavior.” The analysis was based on 30 years of monthly crime and weather statistics for almost 3,000 U.S. counties. The researcher contends that, if the same pattern holds, by the end of the century there will be an additional 22,000 murders, 180,000 cases of rape, 1.2 million aggravated assaults, 2.3 million simple assaults, 260,000 robberies, 1.3 million burglaries, 2.2 million cases of larceny, and 580,000 cases of vehicle theft. 

6. A brand new excuse for bad math grades

In an episode of the long-running urban drama The Wire, a school principal subdues unruly middle schoolers by turning up the heat in classrooms, making them too tired to be rambunctious. It's not a flight of fancy: Children’s math test performance drops as temperatures rise, making the question of which classrooms have air conditioning an issue not only of  comfort but also of academic performance.

Carleton math tests
SOURCE: Tamma Carleton and Solomon Hsiang; journal Science

7. The big whopper

Climate change currently retards potential economic growth by about 0.25 percent a year, every year. Future warming may bring an additional 0.28 percent slowdown annually. Different national economic responses to rising temperatures document the same pattern: “If someone asked me which keeps me awake at night,” Hsiang said, “that’s the thing.”

Carleton econ charts
SOURCE: Tamma Carleton and Solomon Hsiang; journal Science

8. It’s not just about us

Carleton and Hsiang focused on an enormous yet limited task: How does climate affect society? A different paper published Thursday in Science asks how the nonhuman world may fare. A team led by Mark Urban of the University of Connecticut reports a lot of work is needed to assess how climate change affects biodiversity. But it’s pretty clear that making sure plants, animals, and microbes are happy in a human-altered ecosystem isn’t just about keeping them healthy: It’s a critical to our survival, too.