Tom Matthews: Think it's too hot in Europe? Elsewhere, the limit of overheating of the human body has already been reached

Today, it is pretty clear that extreme heat is very likely in the kind of changed climate we live in, writes Tom Matthews, a climate science lecturer at Loughborough University, in The Conversation online publication.

My specialty is the study of climate threats. Last week I published a study on the possibility of a catastrophic combination of cyclones and heat waves in the Southern Hemisphere. Yet in recent days, I have been constantly approached not about this threat, but rather about the heatwave and climate change that has hit the UK. I'm always happy to satisfy the public's interest in extreme weather, but there's a risk that the core message about extreme global heat won't get enough coverage.

Today it is quite clear that extreme heat is very likely in such a changed climate in which we live. Yet the message seems to have to be repeated every time the UK breaks into a sweat. Talking about extremely topical local events tends to obscure the critical message about the global threat of extreme heat.

It is clear that 35°C or more is very hot by British standards, but we must not forget that such conditions are familiar to approximately 80 percent of the world's population . The headline-grabbing 46°C that hit our neighbor France recently is indeed unusual, but it is still below the 50°C that hit India at the beginning of the summer , and it seems moderate compared to the 54°C that Pakistan (2017) has had to experience . in) as well as Kuwait (in 2016) . People living in hotter climates can cope better with higher temperatures, but such high heat requires human sacrifices .

Of course, Europeans are also no stranger to a deadly heat wave. The infamous year of 2003 claimed the lives of nearly 70,000 people , in 2010 over 50,000 people died in the western part of Russia. Fortunately, lessons were learned from these disasters and authorities are now much better prepared when a heat wave warning is issued.

But we could also think of even more unfortunate communities that live and operate in extreme temperature conditions. For example, the body of people living in South Asia and along the Persian Gulf, despite the fact that the heat exchange of the human body is remarkably efficient , is constantly close to the upper limit.

Yes, there is absolutely such a limit.

When the air temperature exceeds 35°C, the body starts evaporating water to maintain its own temperature at a safe level, mainly in the form of sweating. This system works until the "wet thermometer" also reaches 35°C. The temperature of the wet thermometer takes into account the cooling effect of the water evaporating from the thermometer, which is why under normal conditions it is much lower than the normal ("dry thermometer") temperature that we can hear in the weather report.

If the threshold of the wet thermometer is exceeded, the air is so saturated with water vapor that sweat is no longer released. When our body can no longer expel heat, its temperature begins to rise regardless of how much water we drink, how hard we try to stay in the shade, or how much we try to be inactive. Unrelieved, death follows, which primarily affects the very young, the very old, or people with health problems.

Wet-bulb temperatures exceeding 35°C have not been reported yet, but there are some reports that they have started to occur in Southwest Asia. Climate change may be accompanied by the prospect that some very densely populated regions of the globe will cross this threshold before the end of the century, in particular the Persian Gulf region , South Asia and, apparently, the Great China Plain as well. Together, billions of people live in these regions.

When a heat wave hits the UK and other similar areas, people take sensible measures to cope with the heat: move more slowly, drink more water, seek cooler shelter. Air conditioners represent one of the last lines of defense, but they come with their own problems, such as high energy consumption. According to estimates, cooling systems in 2050 will already require as much electricity as the US, EU and Japan together currently produce.

Provided that electricity production can be kept up, it may even be possible to live in a future chronically overheated climate. But when we are so dependent on life-sustaining systems, even an extended power outage can be catastrophic.

A killer combination

So what happens when extreme temperatures and a massive power outage coincide? Recently, I and two colleagues investigated the possibility of such a "grey swan" scenario (a possible but not yet fully realized event) as part of a global study of storms and heat, the results of which were published in the journal Nature Climate Change .

We looked at tropical cyclones that have already caused some of the worst power outages on Earth , the most severe of which was the months-long blackout in Puerto Rico after Hurricane Maria. We found that as the climate warms, it becomes increasingly likely that powerful cyclones will be followed by dangerous heat, and that such complex threats can be expected every year if global warming reaches four degrees. In this case, when dealing with the consequences of a tropical cyclone, ensuring adequate coolness must be given the same importance as ensuring clean drinking water.

The movement of human masses makes extreme heat a global problem.

The UK is entering entirely new territory when it comes to dealing with extreme heat. However, in places that already suffer from heat, the greatest absolute increase in humidity and heat is expected, while reaching the physical limit is not far away . At the same time, they are often the least prepared to face the threat in the region. Therefore, it is not surprising that extreme heat sets migration flows in motion . The movement of human masses makes extreme heat a global problem. Little Britain will feel the effects of changing conditions far from its temperate border.

The trials ahead are severe. Adaptation has its limits. Therefore, we must keep the global perspective firmly in mind and strive towards global cooperation, cutting greenhouse gas emissions at least to the limits of the Paris climate agreement. This gives us the best chance to avoid the killing heat both at home and in the rest of the world.