The incidence of violence, crime, and suicide all rise along with the temperature. During heatwaves, researchers have observed an upsurge in hate speech on Twitter as well as online hostility and language associated with anxiety and sadness.

When we are annoyed, we get “hot under the collar,” when we are angry, our “blood boils,” and when something gets to be too much, we need to “let off steam,” our language itself catches the confluence of heat and emotion. In 1989’s Do The Right Thing, Spike Lee’s groundbreaking examination of racial tension takes place on the hottest day of the year, when sweltering temperatures fuel violent reactions. The intricate relationship between excessive heat and poor mental health outcomes is now beginning to be understood by medical professionals and scientists.

It is becoming more and more necessary to comprehend how high temperatures affect the brain and, more significantly, how we can protect ourselves and others as another early-season heatwave batters the U.S. northwest, with experts expecting more heatwaves for the summer to come. “It is simple to comprehend how experiencing a terrible event like a hurricane can affect mental health. According to Shabab Wahid, a mental health specialist at Georgetown University’s Department of Global Health, the link between heat and mental illness is not immediately obvious.

Wahid recently co-authored a study that was published in The Lancet Planetary Health that demonstrated how even a one degree increase in ambient temperature above average increases the likelihood of developing sadness and anxiety. Although his study concentrated on Bangladesh, he claims that the conclusions are universal. “A increasing corpus of scientific literature has established this connection between climate-related issues and unfavorable outcomes for mental health. And all signs point to these connections being stronger as the effects of climate change deepen.

In fact, a 2018 study by Stanford economist Marshall Burke, published in Nature Climate Change, found a correlation between a 1.8°F (1°C) rise in average temperature in the United States and Mexico and a 1% rise in suicides, which translates to thousands more fatalities every year. According to the Burke study, the combined efforts of suicide prevention initiatives and gun control laws in the United States will be rendered ineffective if temperatures continue to rise as climate scientists anticipate they would.

According to Robin Cooper, an associate clinical professor at the University of California San Francisco and the leader of the Climate Psychiatry Alliance, the number of extreme heat days is rising every year as a result of climate change, fundamentally altering social interactions and personal wellbeing and posing a serious threat to mental stability. “We need to start considering climate change as a crisis in mental health. We are failing in our duty to offer healthcare if we disregard climate change as a threat to the public’s health. Increased research spending is necessary.

Heat affects how the brain functions, although the precise mechanisms are not fully understood. Numerous interconnected psychological, social, and biological issues, such as disturbed sleep and altered neurotransmitter and hormone function due to heat, are cited by scientists.

Josh Wortzel, who studies climate change, heat waves, and mental health at Brown University, says that increases in suicides, mania, and post-traumatic stress disorder (PTSD) tend to happen in late spring and early summer, when temperatures are more unpredictable. “It’s not the hottest days of the year that are linked to the most suicides and suicide attempts,” he says. “Instead, it’s when the temperature changes a lot.” Most of the time, the most dangerous changes are big ones, like this week’s 15°-30°F temperature jump in parts of the Pacific Northwest.

A lot of that comes from not getting enough sleep. Anyone who has lived through a heat wave without air conditioning knows how hard it is to get a good night’s sleep. Cooper says that the effects can add up over time and make people forget things, lose focus, and get more angry. “Sleep is a very complicated process, and not getting enough restful sleep can hurt your mental health in so many ways.” She says that people with bipolar disease often have manic episodes when they don’t get enough sleep, which shows that sleep plays an important role in controlling mood. “Bad sleep may be one of the main reasons” why there is a link between days with high temperatures and mental health problems.

Wortzel says that heat also affects the neurotransmitter serotonin. Serotonin is one of the most important chemicals that controls our moods and is linked to keeping our anger in check. Serotonin helps send information about the temperature of the skin to the hypothalamus in the brain. The hypothalamus then controls whether or not you shiver or sweat. People with depression often have trouble with this process of thermoregulation. The fact that these problems can be helped by taking selective serotonin reuptake inhibitor antidepressants shows that heat exposure and serotonin production are related.

Brit Wray, who is in charge of the program on climate change and mental health at Stanford Medical School, says that climate stress also plays a big role. “It’s not as if everyone who lives through a blaze will get PTSD. But it’s much harder when rains come and wash away everything that was left. And then you have to deal with other social stresses, like a recession or a disease.” Mental system stresses that build up over time make people less resilient. When this happens, unhealthy ways of dealing like drug use, domestic violence, and thoughts of suicide take root. When you add in the neurophysical effects of high heat on the brain and the real danger that heat waves pose to people who already have mental health problems, the effects on mental health get worse. “It becomes a vicious cycle,” says Wray at the 2023 Frontiers Forum, a yearly event that focuses on society, health, and science. “We do have a mental health crisis on top of the climate crisis, and we need to do something about it before too many bad things happen at once.” This means that groups that are most affected will get better help and we will learn more about how climate change, trauma, and mental health are all connected.

Wortzel says that in the past few years, psychologists have become more interested in how changes in temperature and climate affect mental health. The problem is that there isn’t enough money for more study. “Climate change is now seen as the most important issue for public health. But people don’t know enough about how it affects mental health. It’s a shame that we aren’t spending more money right now to learn more about how heat affects the brain. This is bad for study, but it is also bad for the billions of people who will be at risk from extreme heat in the years to come. Heat waves are inevitable in a world that is getting hotter, and more study can help us get ready.