Unbearable Temperatures

 This week in the Pacific north-west, temperature records were being broken. Temperatures reached 47.9C in British Columbia, Canada, temperatures more typically found in the Sahara desert, dozens have died of heat stress, with “roads buckling and power cables melting”.

Another heatwave earlier in June saw five Middle East countries top 50°C. The extreme heat reached Pakistan, where 20 children in one class were reported to have fallen unconscious and needed hospital treatment for heat stress. 

Additional warming from greenhouse gas emissions means that such extreme heatwaves are more likely and scientists can now calculate the increase in their probability. For example, the 2019 European heatwave that killed 2,500 people was five times more likely than it would have been without global warming.

Extreme heatwaves outside the usual range for a region will cause problems, from disrupting the economy to widespread mortality, particularly among the young and old. Yet in places in the Middle East and Asia, something truly terrifying is emerging: the creation of unliveable heat.

While humans can survive temperatures of well over 50C when humidity is low, when both temperatures and humidity are high, neither sweating nor soaking ourselves can cool us. What matters is the “wet-bulb” temperature – given by a thermometer covered in a wet cloth – which shows the temperature at which evaporative cooling from sweat or water occurs. Humans cannot survive prolonged exposure to a wet-bulb temperature beyond 35C because there is no way to cool our bodies. Not even in the shade, and not even with unlimited water.

A 35C wet-bulb temperature was once thought impossible. But last year scientists reported that locations in the Persian Gulf and Pakistan’s Indus River valley had already reached this threshold, although only for an hour or two, and only over small areas. As climate change drives temperatures upwards, heatwaves and accompanying unliveable temperatures are predicted to last longer and occur over larger areas and in new locations, including parts of Africa and the US south-east, over the decades to come.

 Heatwaves intensify inequality. Poorer neighbourhoods typically have fewer green spaces and so heat up more, while outdoor workers, often poorly paid, are especially vulnerable. The rich also buy up cooling equipment at high prices once a heatwave is underway and have many more options to flee, underscoring the importance of public health planning.

Heat can cause havoc with crop production. In Bangladesh, just two days of hot air in April this year destroyed 68,000 hectares of rice, affecting over 300,000 farmers with losses of US$39m (£28m). 

Canada is a warning: more and more of the world will soon be too hot for humans | Simon Lewis | The Guardian