July 3, 2024 -- Climate change is hitting us hard, even in ways we don’t notice. It could be what you see right outside your window, or it could be things your body reacts to that you can’t see. And a lot of us are finally acknowledging its toll: 64% of Americans say they’re worried about climate change, and 1 in 10 report symptoms of anxiety or depression due to climate change, leading some to seek help.
But even if you haven’t been through the trauma of a wildfire or hurricane, or lost sleep fretting for the climate’s future, research suggests that climate change may be affecting your mental health and well-being in other, less obvious ways.
Heatwaves and dust storms may cause irritability and aggression. Air pollution has been linked to depression and psychotic disorders. And rising carbon dioxide (CO2) levels can impair our ability to think.
Climate change is "really an experiment that humanity is running on itself,” said Michael Ranney, PhD, a cognitive psychologist at the University of California, Berkeley.
According to NASA, last summer was the hottest since global records began in 1880. Now we may be amid another record breaker. So it’s a good time to educate yourself on the potential mental health consequences of extreme heat – and air pollution and high CO2 – and learn how to protect yourself.
Hot Enough to Fry Your Mood
A 2022 study showed that on extremely hot days, more people visit hospital emergency rooms for mental health problems like anxiety, schizophrenia, self-harm, and child behavioral disorders. Suicides go up during heatwaves. A recent meta-analysis suggested that for each 1.8-degree Fahrenheit increase in the local temperature, suicides rise by 1%.
Heatwaves may also make us more irritable and prone to violence. In the 1800s, Belgian astronomer Adolphe Quetelet noticed that whenever heat smothered France, violent crime would surge.
Today, there are dozens of studies linking heat with homicides and assaults, said Craig Anderson, PhD, a psychologist at Iowa State University. A 2023 study of Chicago linked extreme heatwaves to surges in crime. In a 6-year study of about 4 billion tweets on Twitter, now called X, the number of hate messages increased with extreme temperatures.
And it’s not just humans who become hostile and agitated in extreme heat. Dogs are more prone to biting on hot, sunny days, while other species, from magpies to bumblebees, become confused and function poorly.
Granted, most research on extreme heat and mental health looks at the relationship between, say, weather data and crime stats, but it can’t prove cause-and-effect. Experimental studies are few. In one, police officers training in an uncomfortably hot room were more likely to draw and fire their weapons than their colleagues training in cooler conditions.
Such studies are complicated and expensive and can be unethical, Anderson said. No one wants to subject volunteers to extreme heat, give them weapons, and see what happens.
Yet certain physiological mechanisms provide a biological basis for emotional changes in heat. For one, we tend to sleep worse when the mercury is high, and “sleep is very closely linked to mental health outcomes,” said Emma Lawrance, PhD, a clinical neuroscientist at the Imperial College London. A 2021 review linked restless nights to more frequent negative moods, increased irritability, and deterioration of mental health conditions such as schizophrenia.
Several hormones may play a role, too. In general, heatwaves mean higher air concentrations of ozone, a molecule that causes the release of stress hormones cortisol and adrenaline. High temperatures may affect other mood-related neurotransmitters, such as serotonin and dopamine. Finnish scientists discovered that as crime levels rise with temperatures, the criminal offenders also experience changes in the serotonin system, possibly increasing impulsivity.
What to Do:
Protect yourself from the heat, especially at night, Lawrance said. Some research-backed ways include taking a lukewarm or cool (but not cold) shower to induce sleep — or at least soaking your feet in lukewarm water. Wearing cotton pajamas and avoiding alcohol before bed can help too. And staying hydrated throughout the day can help your body regulate its temperature more effectively at night.
During heatwaves, pay attention to your irritability. “Be mindful that your mood and thinking may be affected, and be gentle with yourself and loved ones,” Lawrance said.
Know that some mental health medications – such as tricyclic antidepressants and psychotropic drugs -- “can interfere with the body's ability to regulate temperature,” Lawrance said, potentially making the heat’s effects worse. “While it's very, very important people continue to take their medication, it's very important people also have the right information about how to keep themselves safe,” Lawrance said. In other words: Talk to your doctor.
Brain Pollution
Climate change can impact air quality, which may affect mental health, too. Sandstorms, windblown dust from droughts, and wildfire smoke add to the unhealthy soup of pollutants we breathe in, which includes fine particulate matter, or PM 2.5, and nitrogen dioxide (NO2).
A 2023 study that analyzed hospital admissions for psychiatric disorders in eight U.S. states -- Arizona, Maryland, Michigan, New York, New Jersey, North Carolina, Rhode Island, and Washington -- found that the more NO2 and PM 2.5 that floated in the air, the more the emergency rooms filled up with people seeking help for anxiety, bipolar disorder, and schizophrenia. Air pollution has also been linked to depression and lower mental performance. Research suggests it may lead to unethical behaviors such as cheating on tests.
When pollutants such as PM 2.5 enter our body, they induce oxidative stress and inflammation, which can kill brain cells. Several studies have found that air pollution is associated with damage of certain brain regions such as the amygdala, the brain’s fear center, and the hippocampus, a seahorse-shaped area involved in the development of depression.
What to Do:
If you’re concerned, you can check the Environmental Protection Agency's AirNow site for up-to-date air quality information. When air quality is low, such as during wildfires, keep windows closed and stay indoors if you can.
“When [you’re] outdoors in intense wildfire smoke, it is best to wear a good-fitting N95 or KN95 mask, which will filter out most of the PM 2.5,” said Paul Wennberg, PhD, an atmospheric chemist at California Institute of Technology in Pasadena. Indoors, you can use a portable air cleaner or a high-efficiency HVAC filter. (No air cleaner? You can make a DIY version using instructions on the EPA’s website.) Avoid making your indoor air worse on high pollution days: Try not to toast bread, fry food, or burn candles.
Extreme weather events, such as hurricanes, can also stir up brain-harming pollutants in the water we drink and the earth where we grow our food. Hurricane Harvey left soils around Houston contaminated with heavy metals such as lead, while Hurricane Maria added several pesticides and arsenic to Puerto Rico’s drinking water.
Lead has long been linked to cognitive challenges — from lower IQ to depression and mania. Other heavy metals, such as cadmium, are associated with mental health disorders. As such, drinking bottled water is recommended after hurricanes.
Cognitive Effects of High CO2
As climate change progresses, rising carbon dioxide levels are an obvious marker. What’s less obvious is how CO2 increases can affect our ability to think.
“It's another, indirect reason to not want to burn fossil fuels,” Ranney said. CO2 concentration in the atmosphere has already increased from about 280 ppm in pre-industrial times (mid-1700s) to 419 ppm in 2023. At this rate, it could more than double by the year 2100, exceeding 900 ppm.
Lab experiments show that such high doses of CO2 may impact how clearly we think. In one study, people’s decision-making suffered when they were exposed to 1,000 ppm CO2 – they were less flexible in solving problems and had trouble using information to make a decision. In another, a 400 ppm increase in CO2 was associated with a 21% decrease in cognitive function (the ability to learn, think, and reason).
As Ranney points out, volunteers in these experiments are exposed to high CO2 for short periods of time — say, a couple of hours. "If that can diminish one's cognitive performance, imagine what it's like if you never have a respite,” he said.
Ranney suspects that human cognition may already be impacted by the atmosphere’s heightened CO2. And the higher the CO2 level is outside, the harder it is to keep air fresh inside, where CO2 can easily climb to more than 1,000 ppm.
What to Do:
Although we can’t simply scrub CO2 out of the air, we can try to keep indoor levels as low as possible.
Use a carbon dioxide monitor, and if the levels exceed 1,000 ppm, open the windows if air quality is not bad that day. Avoid using unvented or poorly vented fuel-burning appliances, such as gas stoves or space heaters. Some studies also suggest that potted plants may help reduce CO2 levels at home, especially if provided with plenty of light.
Still, while these tips can help you protect yourself, what we really need, Lawrance said, is urgent action on climate change. “Creating a world that is cleaner is … much better for our mental health,” she said.
