How Extreme Heat and Humidity Are Pushing the Limits of Human Survival: QuickTake
The world touched a global record on July 3, the hottest day ever, as climate change raises temperatures. Heat waves are also more frequent and more acute. Factor in humidity, and extreme weather is already testing the limits of the human body. Last year, when blistering heat hit India, Pakistan, Bangladesh, Nepal and Sri Lanka, New Delhi recorded peaks of more than 49C (120F). This year, parts of India again hit sweltering pre-monsoon temperatures grim news for power grids, crops and hundreds of millions of workers, though figures on fatalities remain unclear. Elsewhere, a punishing heat dome covered Texas and northern Mexico. Unusually hot and dry conditions are forecast into the summer in Europe as well. 1. What makes extreme heat so dangerous? Many reasons. People are more likely to dehydrate in high temperatures, increasing the risk of heart attack and stroke. Heat can worsen breathing problems, especially where pollution levels are elevated. Heat stress makes it harder for people to work and increases the likelihood of injuries. Its hard to know exactly how many people die from heat each year; most go uncounted. Theres no official toll from the 2022 scorcher in India and Pakistan, but early tallies of about 90 deaths are almost certainly too low. 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, elevating overnight temperatures and contributing to heat stress. Women and seniors were found to be the most affected populations in one 10-year study of extremely hot weather events conducted in Hong Kong. 2. Whats wet-bulb temperature? Forecasters are increasingly using measures of heat stress and discomfort like humidex, heat index or apparent temperature to understand the health risks posed by high temperatures. Wet-bulb 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 think Phoenix, Ariz., in July 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. Thats high enough to trigger heatstroke even for healthy people with unlimited shade and water. In reality, shade and water are often limited, and heat can kill at much lower wet-bulb temperatures. A 2020 study published 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 were no greater than 28C. 3. How are wet-bulb temperatures measured? Originally by wrapping a wet cloth around the bulb of a thermometer. Scientists would record the level after moistures 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 tool to forecast a more advanced metric of heat stress, the wet-bulb globe temperature, which factors in wind speed, sun angle and cloud cover. 4. Where is this a problem? 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. An El Nino weather pattern is pushing the mercury to unprecedented levels in the region. Parts of Pakistan, the Middle East and Mexico are also likely to experience extreme heat and high humidity. But increasingly, typically temperate places are also seeing incredibly hot days. The UK registered a record of 40.3C in July 2022 and places in Portugal hit 47C, but relatively low humidity in both places kept the wet-bulb temperature around 25C. Spain and Portugal recorded their hottest April on record this year as a mass of hot air brought temperatures close to 40C in some areas at the end of the month. The heat wave happened amid a widespread drought thats hitting the region for the second consecutive year. 5. What is the economic and social impact of heat? In places with extreme heat, every aspect of life becomes more challenging, and inequalities become more acute, especially in cities. But even cooler places feel the effects, typically through higher food and energy prices. For example, Indias scorching summer of 2022 curtailed wheat production and forced the worlds second-largest producer to ban exports, which stoked fears of global food shortages and inflation amid the war in Ukraine, even though India is not a major exporter. (In the end India was set to harvest a record wheat crop.) Similar strain this year could again affect wheat, rapeseed and chickpeas. Previous El Ninos resulted in a marked impact on global inflation, 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 pockets as prices rise. Heat also exacerbates drought, adding further stress to hydropower and nuclear power production. 6. How is extreme heat related to climate change? A new branch of science, extreme event attribution, connects global warming to severe episodes of weather with a degree of specificity. Heat waves are most directly linked to humanitys 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 two months longer than it was in the 1970s and 1980s.) Global warming is making tropical cyclones also called hurricanes or typhoons more intense. Warmer water and moister air two results of global warming provide added fuel to such storms, such as the monster cyclone that hit Western Australia in April. In India and Pakistan, extreme heat is 30 times more likely due to a changing climate. --With assistance from Eric Roston and Brian K. Sullivan. More stories like this are available on bloomberg.com 2023 Bloomberg L.P.