‘Everybody has a breaking point’: how the climate crisis affects our brains
In late October 2012, a category 3 hurricane howled into New York City with a force that would etch its name into the annals of history. Superstorm Sandy transformed the city, inflicting more than $60bn in damage, killing dozens, and forcing 6,500 patients to be evacuated from hospitals and nursing homes. Yet in the case of one cognitive neuroscientist, the storm presented, darkly, an opportunity.
Yoko Nomura had found herself at the centre of a natural experiment. Prior to the hurricane’s unexpected visit, Nomura – who teaches in the psychology department at Queens College, CUNY, as well as in the psychiatry department of the Icahn School of Medicine at Mount Sinai – had meticulously assembled a research cohort of hundreds of expectant New York mothers. Her investigation, the Stress in Pregnancy study, had aimed since 2009 to explore the potential imprint of prenatal stress on the unborn. Drawing on the evolving field of epigenetics, Nomura had sought to understand the ways in which environmental stressors could spur changes in gene expression, the likes of which were already known to influence the risk of specific childhood neurobehavioural outcomes such as autism, schizophrenia and attention deficit hyperactivity disorder (ADHD).
The storm, however, lent her research a new, urgent question. A subset of Nomura’s cohort of expectant women had been pregnant during Sandy. She wanted to know if the prenatal stress of living through a hurricane – of experiencing something so uniquely catastrophic – acted differentially on the children these mothers were carrying, relative to those children who were born before or conceived after the storm.
More than a decade later, she has her answer. The conclusions reveal a startling disparity: children who were in utero during Sandy bear an inordinately high risk of psychiatric conditions today. For example, girls who were exposed to Sandy prenatally experienced a 20-fold increase in anxiety and a 30-fold increase in depression later in life compared with girls who were not exposed. Boys had 60-fold and 20-fold increased risks of ADHD and conduct disorder, respectively. Children expressed symptoms of the conditions as early as preschool.
“Our findings are extremely alarming,” the researchers wrote in a 2022 study summarising their initial results. It is not the type of sentence one usually finds in the otherwise measured discussion sections of academic papers.
Yet Nomura and her colleagues’ research also offers a representative page in a new story of the climate crisis: a story that says a changing climate doesn’t just shape the environment in which we live. Rather, the climate crisis spurs visceral and tangible transformations in our very brains. As the world undergoes dramatic environmental shifts, so too does our neurological landscape. Fossil-fuelinduced changes – from rising temperatures to extreme weather to heightened levels of atmospheric carbon dioxide – are altering our brain health, influencing everything from memory and executive function to language, the formation of identity, and even the structure of the brain. The weight of nature is heavy, and it presses inward.
Evidence comes from a variety of fields. Psychologists and behavioural economists have illustrated the ways in which temperature spikes drive surges in everything from domestic violence to online hate speech. Cognitive neuroscientists have charted the routes by which extreme heat and surging CO2 levels impair decision-making, diminish problem-solving abilities, and short-circuit our capacity to learn. Vectors of brain disease, such as ticks and mosquitoes, are seeing their habitable ranges expand as the world warms. And as researchers like Nomura have shown, you don’t need to go to war to suffer from post-traumatic stress disorder: the violence of a hurricane or wildfire is enough. It appears that, due to epigenetic inheritance, you don’t even need to have been born yet.
When it comes to the health effects of the climate crisis, says Burcin Ikiz, a neuroscientist at the mental-health philanthropy organisation the Baszucki Group, “we know what happens in the cardiovascular system; we know what happens in the respiratory system; we know what happens in the immune system. But there’s almost nothing on neurology and brain health.” Ikiz, like Nomura, is one of a growing cadre of neuroscientists seeking to connect the dots between environmental and neurological wellness.
As a cohesive effort, the field – which we might call climatological neuroepidemiology – is in its infancy. But many of the effects catalogued by such researchers feel intuitive.
Perhaps you’ve noticed that when the weather gets a bit muggier, your thinking does the same. That’s no coincidence; it’s a nearly universal phenomenon. During a summer 2016 heatwave in Boston, Harvard epidemiologists showed that college students living in dorms without air conditioning performed standard cognitive tests more slowly than those living with it. In January of this year, Chinese economists noted that students who took mathematics tests on days above 32C looked as if they had lost the equivalent of a quarter of a year of education, relative to test days in the range 22–24C. Researchers estimate that the disparate effects of hot school days – disproportionately felt in poorer school districts without access to air conditioning and home to higher concentrations of nonwhite students – account for something on the order of 5% of the racial achievement gap in the US.
Cognitive performance is the tip of the melting iceberg. You may have also noticed, for example, your own feelings of aggression on hotter days. You and everyone else – and animals, too. Black widow spiders tend more quickly toward sibling cannibalism in the heat. Rhesus monkeys start more fights with one another. Baseball pitchers are more likely to intentionally hit batters with their pitches as temperatures rise. US Postal Service workers experience roughly 5% more incidents of harassment and discrimination on days above 32C, relative to temperate days.
Neuroscientists point to a variety of routes through which extreme heat can act on behaviour. In 2015, for example, Korean researchers found that heat stress triggers inflammation in the hippocampus of mice, a brain region essential for memory storage. Extreme heat also diminishes neuronal communication in zebrafish, a model organism regularly studied by scientists interested in brain function. In human beings, functional connections between brain areas appear more randomised at higher temperatures. In other words, heat limits the degree to which brain activity appears coordinated. On the aggression front, Finnish researchers noted in 2017 that high temperatures appear to suppress serotonin function, more so among people who had committed violent crimes. For these people, blood levels of a serotonin transporter protein, highly correlated with outside temperatures, could account for nearly 40% of the fluctuations in the country’s rate of violent crime.
“We’re not thinking about any of this,” says Ikiz. “We’re not getting our healthcare systems ready. We’re not doing anything in terms of prevention or protections.”
Ikiz is particularly concerned with the neurodegenerative effects of the climate crisis. In part, that’s because prolonged exposure to heat in its own right – including an increase of a single degree centigrade – can activate a multitude of biochemical pathways associated with neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Air pollution does the same