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The world\u2019s two hottest days\u00a0on record<\/a>\u00a0happened in July and 2024 is on track to be the\u00a0warmest year<\/a>\u00a0ever<\/a>. Heat waves are more\u00a0frequent<\/a>, have been more acute, and often arrived\u00a0earlier than anticipated<\/a>. Factor in humidity, and extreme weather is already testing the limits of the human body. More than\u00a01,300 people died<\/a>\u00a0during the Hajj pilgrimage in Saudi Arabia in June as temperatures reached about 52C (126F), while heat-related fatalities\u00a0have also been recorded<\/a>\u00a0this year in locations including the US, Thailand, India and Mexico. Parts of Europe \u2014 where high temperatures contributed to\u00a0over 47,000 deaths<\/a>\u00a0in 2023 \u2014 remain on alert for more extreme conditions this summer.\u00a0<\/p>\n There are\u00a0many reasons<\/a>. People are more likely to dehydrate in high temperatures, increasing the risk of heart attack and stroke. Heat can worsen breathing problems, especially in places with elevated pollution levels. Heat stress makes it harder for people to work and increases the\u00a0likelihood of injuries<\/a>. It\u2019s hard to know exactly how many people die from heat each year; most\u00a0go uncounted<\/a>. Europe likely experienced 61,672 deaths attributable to heat in 2022, though that number potentially underestimates the actual total,\u00a0according<\/a>\u00a0to a study led by the Barcelona Institute for Global Health. Emerging economies suffer more than developed ones, as there tends to be little respite from the sun; most people work outside and few have effective cooling at home. Concrete and asphalt in urban settings can trap the heat, increasing\u00a0overnight temperatures<\/a>\u00a0and contributing to heat stress.\u00a0Women<\/a>\u00a0and\u00a0seniors<\/a>\u00a0have been found in studies to be the populations most affected by extremely hot weather.\u00a0<\/p>\n Forecasters<\/a>\u00a0are increasingly using measures of heat stress and discomfort \u2014 like\u00a0humidex<\/a>, heat index or apparent temperature \u2014 to understand the health risks posed by high temperatures. \u201cWet-bulb\u201d is one of these measures. It accounts for the effects of humidity, which makes it harder for the human body to cool itself by sweating. For example, 42C with 40% humidity \u2014 think Phoenix, Ariz., in July \u2014 has a wet-bulb temperature around 30C. A lower temperature of, say, 38C, but with higher humidity of 80%, will give a wet-bulb reading around 35C. That\u2019s high enough to trigger heatstroke even for healthy people with unlimited shade and water, and has already\u00a0started to appear<\/a>\u00a0in coastal subtropical regions. In reality, shade and water are often limited, and heat can kill at much lower wet-bulb temperatures.\u00a0A 2020 study<\/a>\u00a0published in the journal Science found regions affected by the 2003 European and 2010 Russian heat waves, which proved deadly for thousands, experienced wet-bulb values no greater than 28C.\u00a0<\/p>\n Originally by wrapping a wet cloth around the bulb of a thermometer. Scientists would record the level after moisture\u2019s vaporization cools it down, the way the body cools down by sweating. Now, wet-bulb temperatures are measured using electronic instruments at weather stations, with further studies of hot spots assisted by satellite data from sources including NASA and the International Space Station. The National Oceanic and Atmospheric Administration in the US also developed a\u00a0tool<\/a>\u00a0to forecast a more advanced metric of heat stress, the wet-bulb globe temperature, which factors in wind speed, sun angle and cloud cover.\u00a0<\/p>\n Traditionally, heat and humidity have been highest in South Asia and subtropical climates. Some places in India have notched wet-bulb temperatures higher than 32C; the UN predicts it will be one of the first countries to surpass a wet-bulb temperature of 35C. Planetary warming and the impact of the\u00a0El Nino weather pattern<\/a>\u00a0mean there\u2019s a high chance temperature and humidity records will be set this year across a sweep of regions straddling the equator, including Florida, Texas, much of Africa, India, Australia, and Central and South America,\u00a0according<\/a>\u00a0to the University of California, Berkeley. Increasingly, typically temperate places are also seeing incredibly hot days. The UK\u00a0registered a record<\/a>\u00a0of 40.3C in July 2022, though relatively low humidity kept the wet-bulb temperature around 25C. Barcelona experienced its\u00a0hottest ever day<\/a>\u00a0in late July. In the US, heat alerts covered about half the population on Aug. 1, the World Meteorologial Organization said.\u00a0Japan, Greece, Hungary and Croatia<\/a>\u00a0were among nations to experience their warmest July on record.\u00a0<\/p>\n In places with extreme heat, every aspect of life becomes more challenging, and inequalities become more acute, especially in cities. But\u00a0even cooler places feel the effects<\/a>, typically through higher food and energy prices. Coffee prices this year surged to a\u00a045-year high<\/a>\u00a0as persistent heat and drought exacerbated a supply crunch in Vietnam, the world\u2019s largest robusta producer. Dry conditions in Russia this year prompted analysts to cut wheat production forecasts, and supply of crops including rapeseed and chickpeas also remains susceptible to the impact of heat. Previous El Ni\u00f1os resulted in a\u00a0marked impact on global inflation<\/a>, adding 3.9 percentage points to non-energy commodity prices and 3.5 points to oil, according to Bloomberg Economics modeling. Power consumption also rises during peak heat, straining the grid and consumers\u2019 pockets as prices jump. Natural gas prices advanced this summer as consumers grappled with blackout risks; Egypt, typically an exporter of the fuel, resorted to buying LNG amid higher demand. Heat also exacerbates\u00a0drought<\/a>, adding further stress to\u00a0hydropower<\/a>\u00a0and\u00a0nuclear power<\/a>\u00a0production. Extreme temperatures pose an increasing threat to outdoor activities, disrupting events including\u00a0concerts<\/a>, religious gatherings, and sporting events.<\/p>\n A new branch of science,\u00a0extreme event attribution<\/a>, connects global warming to severe episodes of weather with a degree of specificity. Heat waves are most directly linked to humanity\u2019s greenhouse gas pollution. And heat, along with dryness and wind, fuels forest fires, which is why scientists are now confident that climate change is exacerbating wildfires in the western US, Australia and elsewhere. (The US fire season is\u00a0two months longer<\/a>\u00a0than it was in the 1970s and 1980s.) Global warming is making\u00a0tropical cyclones<\/a>\u00a0\u2014 also called hurricanes or typhoons \u2014 more intense. Warmer water and moister air \u2014 two results of global warming \u2014 provide added fuel to such storms, such as the\u00a0record-breaking Hurricane Beryl<\/a>\u00a0in July that raged through parts of the Caribbean and US. In India and Pakistan, extreme heat is\u00a030 times more likely<\/a>\u00a0due to a changing climate.<\/p>\n<\/div>\n\nWhat makes extreme heat so dangerous?<\/h2>\n
How is extreme heat measured?\u00a0<\/h2>\n
How are wet-bulb temperatures measured?<\/h2>\n
Where is this a problem?\u00a0<\/h2>\n
What is the economic impact of heat?<\/h2>\n
How is extreme heat related to climate change?\u00a0<\/h2>\n
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