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more vulnerable to damage that can lead to neurodegenerative diseases. Heat also affects the barrier that normally protects the brain, making it more permeable and increasing
the risk that toxins, bacteria and viruses can cross over into our brain tissue.
This could become more important as temperatures increase, as so too will the spread of
mosquitos that transmit viruses that can cause neurological disease, such as Zika, chikungunya and dengue. "The Zika virus can affect foetuses and cause microcephaly," says Tobias
Suter, a medical entomologist at the Swiss Tropical and Public Health Institute. "Rising temperatures and milder winters mean that the mosquito breeding season begins earlier in the
year and ends later." (Read David Cox's story on how the US's mosquito season is already
changing.)
Heatwaves are capable of influencing a whole range of factors, from the electrical firings
of the nerve cells to suicide risk, climate anxiety and even the stability of medication for
neurological conditions.
But exactly how rising temperatures affect our brains are still being investigated by scientists. Heat affects people in very different ways 3 some thrive in hot weather, others find it
unbearable. "Different factors might be relevant for this differential sensitivity, and one of
them may be genetic susceptibility," says Sisodiya. Genetic variants could influence the
structures of proteins that might render some people more vulnerable to the impacts of climate change.
"There may be thermo-latent phenotypes that will only become apparent when those environmental pressures are sufficient to bring them out," he says. "What we're seeing today in
people with neurological disorders could become relevant for people without neurological
disorders as climate change progresses."
There are still other questions that remain to be answered too. For example, is it the maximum temperature, is it the length of a heatwave or the nighttime temperature that has the
greatest impact? It may well differ for each person or by neurological condition.
But identifying who is at risk and why will be crucial to developing strategies to protect the
most vulnerable. These could include early warning systems or insurance to compensate
day labourers for lost wages due to extreme heat.
"The era of global warming has ended, the era of global boiling has arrived," UN SecretaryGeneral Antonio Guterres announced, when July 2023 was confirmed to be the hottest
month on record. Climate change is here and it is intensifying. The era of the hot brain is just
beginning.
