Who faces the highest risk of deadly heat?
Over the last couple of weeks there have been extraordinary heatwaves in North America. Heat records were broken across the Pacific Northwest, with temperatures over 40 degrees C in usually temperate cities such as Portland or Seattle. The full toll is yet to be counted, but authorities in British Columbia are reporting 500 or so heat-related deaths so far. Beyond the human casualties, the total harm of the heat wave will include damage to infrastructure, wildlife, agriculture, and the damage of subsequent wildfires. Nobody has seen anything quite like this before, though heatwaves are becoming more frequent and lasting longer in the region. For usually temperate places, especially inland, extraordinary summer heatwaves may be the most serious and most frequent climate related natural disaster. For warmer regions of the world, temperatures are often higher all year round. Extreme heat isnt just a freak summer occurrence. The risk of extreme heat is more severe, and it can be deadly. The biology of deadly heat is not complicated. The human body maintains a stable temperature of around 37 degrees C. If temperatures rise above that, then the body cant shed excess heat into the surrounding air. We have to keep cool in other ways, such as sweating. If you combine high heat and high humidity, that doesnt work either. Now you need more purposeful interventions  a cold shower, air conditioning. And if youre not able to cool down, or if the electricity supply fails, a medical emergency or even heat death is a real possibility. Parts of the world already tip into deadly extremes on a regular basis. The city of Jacobabad in Pakistan is one of the hottest in the world, with the mercury rising over 50 degrees C at times. It has officially hit unsurvivable temperatures on several occasions, at which point the streets clear, and people hunker down with whatever cooling technologies they can afford. Events in North America show that extreme heat can strike anywhere, but the risk is not evenly distributed. It is far more likely in the Equatorial regions that are already hot. This paper from Nature Climate Change shows the places that will suffer most from high heat under a warming scenario of 2-3 degrees (which is what we are currently on track for.) As with harvest losses and land rendered uninhabitable, theres a visible pattern here. With some exceptions, the majority of the harm of extreme heat falls on places that have done less to cause global climate change. Those regions of the world that have the highest historical emissions, in Europe and North America, are less vulnerable. This is another example of climate injustice and  as I describe in my book, Climate Change is Racist  there is a racial dynamic here. It is consistently people of colour that bear the burden of risk. And that means that preventing runaway climate change will also avert an epic racial injustice.