Why are the north-western United States and British Columbia suffering a heatwave?
LYTTON IS A pretty temperate place. Average daily highs for June are around 16.4C (61.5F). But on June 28th the village reported a high of 47.9C (118.2F)beating its own record from the previous day of 46.6C (115.9F) which, at the time, was 1.6C hotter than any temperature recorded anywhere in Canada, ever. (It was also the highest temperature ever recorded at a latitude above 50 North.) Lytton is not alone. Canadas west coast and much of Americas Pacific north-west are baking in a heatwave. In Vancouver vaccination centres were forced to close or relocate. In Portland, Oregon public transport was partially suspended. The Twitter account for the citys famous streetcars posted a picture of a melted power cable. The Economist Today Hand-picked stories, in your inbox A daily email with the best of our journalism Sign up  The heatwave is caused by a phenomenon known as a heat dome, in which an area of high pressure in the atmosphere stops the air beneath it escaping. Like a lid on a boiling pot, the dome forces air downwards, raising temperatures even further. The one currently hovering over the north-west is extremely unusual in both intensity and durationsuch prolonged recording-breaking heat has not been seen since the heatwaves which caused North Americas dust bowl in the 1930s. But climate change, the consequence of the increase in greenhouse gases in the atmosphere resulting from human activity, is making weather events such as heat domes more likely. One of the main causes of heat domes in North America, according to Americas National Oceanic and Atmospheric Administration, is a sharp difference in temperature between the east and west of the Pacific over the preceding winter. The movements of water that create such gradients may be changing because of global warming, but the link isnt clear. What is undeniable, though, is that a warmer climate overallwith average global temperatures now having risen by at least 1C from pre-industrial levelsmake the temperature spikes experienced in heatwaves that much more unbearable. The north-wests heatwave is all the more troublesome because the regions climate is typically mild. Many homes do not have air conditioning, leading some local governments to set up specialised cooling centres in locations that do, such as stadiums, providing a space where people can work, get water and sleep. Others have lifted covid-19 restrictions at public pools. Meanwhile, power suppliers asked consumers to use less energy to avoid overwhelming the grid. Outdoor activities, including sports matches, have been stopped. Schools have been closed. Although temperatures are expected to subside in the coming week, similar heatwaves may recur throughout the summer. Typically, late July is the warmest time of the year. The plight of North Americas north-west points to a deeper problem. People and infrastructure in urban areas, which absorb more heat than rural ones, are particularly vulnerable to high temperatures. Even in well-off countries, cities are often ill-equipped to cope with extreme heat (exceptions include urban areas in oil-rich Arab states). Keeping people safe in places like Portland has, essentially, meant grinding cities to a halt. Although heatwaves kill more people than more dramatic floods or hurricanes, few governments have policies and dedicated responses to deal with them. Even fewer have worked out how to deal with the inequalities that extreme heat exacerbates: they disproportionately impact those living in low-income areas, without green space, and also pose greater risks to people with poor underlying health. Little is known either about how to prevent the financial consequences of lost productivity. Dangerous heatwaves are still widely regarded as being risks for countries such as India, where spiking temperatures in 2015 killed thousands. But climate change means that more places are more likely to be exposed to themof 122 studies of extreme heat events around the world, more than 90% found that they were worsened or made more probable by climate change. That means countries everywhere have to prepare, and fast.