Climate change: Rising temperatures can have a serious impact on our ability to think
It's time to think about the effects warmer weather is having on our brains, not just our bodies.
The summer of 2022 was Europe’s hottest on record. In the heat I felt foggier and groggier. Thinking felt like hard work. Like many others, on the worst days I hid inside, closed all the curtains, and waited out the heat in the coolest room of my flat. It was in my temperature safe haven I wondered, metaphorically, can our thoughts melt? Or freeze? Said differently, how does the heat in our environment affect our ability to think?
When temperatures are too low or high they become an 'ambient stressor', something in our environment that drains brain energy. There are two major scientific ideas about how this works.
The first is the inverted-U model, which assumes that up to a critical temperature, brain performance increases, and then it immediately drops, in an upside-down U-shape. According to this model, there is a single temperature at which the brain and body work the best: 21.6°C.
The second is the maximal adaptability model, which proposes a plateau instead of a single optimal temperature. In this model, there is a range of best temperatures for the brain.
A group of researchers who reviewed many studies on how heat affects cognition in 2019 found that the Maximal Adaptability Model better fits the data better than the inverted-U model. In these studies, participants – who were most often men – were typically put an ambient chamber, a purpose-built room with temperatures that can be programmed up to 50°C.
That’s a lot cooler than your average Swedish sauna, which is typically over 70°C, but a lot hotter than the “'neutral' 21.6°C. Other researchers immersed participants in hot water, or dressed people in a special tube-lined heat-controllable suit. Once they were appropriately cold or hot, participants were given attention, memory, and problem-solving tasks.
This research has broadly found that our cognitive comfort zone is between 21.1°C and 26.6°C. Within this range heat doesn’t impact our ability to think. When we move outside of this comfort zone, we start to get groggier. After we hit the edge of our zone of maximal adaptability, that we start to really see a difference. Once temperatures either drop below 10°C, or get hotter than 32.2°C, our performance falls off a cliff. It takes us far more energy to pay attention, remember things, and think.
For many people, staying in a space that is under 32.2°C will probably be safe for their brains. However, those with psychological conditions like dementia, depression, and schizophrenia, often have a significantly increased vulnerability to extreme heat, already seeing big increases in hospitalisations above 26.7°C.
If you are exposed to even more extreme temperatures, you can enter a dangerous state of hypothermia if your core body temperature drops too far, or hyperthermia (heat stroke) if it gets too hot. These can make you confused, cause permanent damage to attention and memory, and can be life threatening. In these circumstances, getting people out of the heat, specifically icing the neck and head as soon as possible, can prevent long-term consequences to our fragile brains.
There are some people who can’t choose whether to escape the heat. These include firefighters, professional athletes, soldiers, and miners. In some of these settings, wearable neck and head cooling devices, and the more classic ice baths, are currently being used to tackle hot brains and prevent damage. For cold conditions, wearable heated clothing and warmed blankets help warm up our brains.
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A study carried out in Guangzhou, China, on the impact of hot weather on work-related injuries, found that with every 1°C increase in temperature there was a 1.4 per cent increase in daily injury claims. This accident proneness starts right at the edge of our comfort zones, at a temperature of about 26°C. As our decision-making melts, we are more likely to make bad calls and injure ourselves.
Every person feels the heat differently, and all our bodies are different at regulating it. Adjusting to our changing climate will be necessary to keep our brains sharp. If you find that your mind is freezing, or melting, find a space between 10°C and 26°C and you should get back to your intelligent self in no time.
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Dr Julia Shaw is a research associate at University College London and the co-host of the Bad People podcast on BBC Sounds. She is an expert on criminal psychology, and the author of three books, Bi: The hidden culture, history, and science of bisexuality, Making Evil: The Science Behind Humanity’s Dark Side and The Memory Illusion: Remembering, Forgetting, and the Science of False Memory.