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Gizmodo
2 days ago
- Climate
- Gizmodo
Deadly ‘Wet-Bulb' Temperatures Are Smothering the Eastern U.S.
An oppressive heat dome has gripped the eastern U.S. this week, prompting the National Weather Service (NWS) to issue heat warnings for nearly 170 million Americans. To make matters worse, severe humidity is making high temperatures feel even hotter. Extreme heat and humidity make for a deadly combination. The human body lowers its temperature by sweating, and when sweat evaporates, it cools the surface of the skin. Humidity slows this process down, increasing the risk of heat-related illness. To extrapolate the combined physiological impact of heat and humidity, meteorologists look at the wet-bulb temperature. This measurement essentially represents the amount of heat stress the body experiences under hot, humid conditions. It's also a critical metric for understanding human survivability in a changing climate. 'The wet-bulb temperature is literally the temperature of a wet thermometer's bulb, traditionally measured by putting a tiny wet sock on the end of a thermometer,' David Romps, a professor of Earth and planetary science at the University of California-Berkeley, told Gizmodo in an email. Similar to a sweating person, the wet-bulb thermometer cools itself by evaporating water, 'but a wet-bulb thermometer is not like a person in some important ways,' he explained. Humans generate body heat, which must dissipate into the air. 'Therefore, all else equal, a sweaty person will be warmer than a wet bulb,' Romps said. When the wet-bulb temperature approaches 98.6 degrees Fahrenheit (37 degrees Celsius)—the average human body temperature—it's extremely difficult to maintain a safe internal temperature. This may lead to severe heat-related illness or even death, he explained. Experts have long believed that a wet-bulb temperature of 35 degrees Celsius (equal to 95 degrees Fahrenheit at 100% humidity or 115 degrees Fahrenheit at 50% humidity) was the threshold at which the human body can no longer cool itself. In recent years, however, researchers have found evidence to suggest that this threshold is actually much lower. 'Based on our research, a wet bulb temperature of around 87 degrees Fahrenheit [30.6 degrees Celsius] at 100% humidity is the critical threshold above which humans cannot maintain a stable core temperature if they were exposed to those conditions for hours at a time,' Kat Fisher, a PhD candidate in the human thermoregulatory lab at Penn State University, told Gizmodo in an email. Taking the wet-bulb temperature into account with air temperature, wind speed, cloud cover, and the angle of the Sun gives meteorologists the wet-bulb globe temperature (WBGT), a comprehensive measure of heat stress in direct sunlight. On Tuesday, July 29, the NWS reported WBGT values in the high 80s to low 90s Fahrenheit (upper 20s to mid-30s Celsius) across much of the eastern U.S., particularly in the Southeast and Midwest. WBGT values above 90 degrees Fahrenheit (32 degrees Celsius) are extreme and can induce heat stress in just 15 minutes when working or exercising in direct sunlight, according to the NWS. Weather officials expect these conditions to persist through Wednesday, July 29, before the heat dome dissipates later in the week. Over the long term, dangerous wet-bulb temperature events are here to stay. 'Human-caused global warming is driving up wet-bulb temperatures, pushing even healthy people closer to their physiological limit. And that limit is real,' Romps said. The human body is physiologically incapable of withstanding wet-bulb temperatures around or above its internal temperature, he explained. As the atmosphere warms, it can hold more moisture, increasing the frequency and intensity of extreme wet-bulb temperatures. Climate models suggest that certain regions of the world could see wet-bulb temperatures regularly topping 95 degrees Fahrenheit (35 degrees Celsius) within the next 30 to 50 years, according to NASA. In the U.S., Midwestern states like Arkansas, Missouri, and Iowa will likely hit the critical wet-bulb temperature limit within 50 years. 'Throughout the 300,000 years of our species, there has been no need to tolerate such wet-bulb temperatures because it is likely they never occurred as a normal part of weather throughout that time,' Romps said. 'Global warming is changing that, and fast.' Extreme heat is already the deadliest weather hazard in the U.S. Data from the Centers for Disease Control and Prevention (CDC) show that roughly 2,000 Americans die from heat-related causes per year, ABC News reports. Some experts believe the death toll is grossly underestimated. Understanding the limits of human survivability in a warmer world is literally a matter of life or death. There is an urgent need to adapt infrastructure, public health systems, and extreme heat response measures to the changing climate.
National Observer
08-07-2025
- Science
- National Observer
Lightning strikes the Arctic: What will it mean for the Far North?
So far, the detection networks that count lightning strikes around the world have seen only a vague hint of an upwards trend in total global lightning. But in the north, the story is different. In the Arctic, there has been a far more dramatic upsurge, with one report finding that north of the 80th parallel (passing through the top of Greenland), recorded lightning events went from around 100 per year in the early 2010s to more than 7,000 in 2021. Historically, 'the Arctic basically didn't have lightning at all,' says Robert Holzworth, a retired atmospheric physicist with the University of Washington in Seattle. 'Now it's got a lot more. It's easy to see that.' Researchers are now scrambling to get a better sense of how much lightning will increase in the north, and what that will mean for people, local ecosystems, and the global climate. Will more lightning spark more fires, or will more rain — also brought by climate change — dampen them? And is what's happening in the north an aberration, or does it signal change across the rest of the planet? In 2014, UC Berkeley atmospheric scientist David Romps famously calculated that lightning strikes increase by about 12 percent per degree Celsius of global warming, which could add up to a 50 percent increase by 2100. This estimate was based on just two main factors, which Romps showed were tightly linked to lightning across the continental United States: precipitation and 'convective available potential energy,' a measure of air instability. More rainclouds (with water and ice particles bumping up against each other to create electric charge) and more convection beget more lightning. But as scientists have considered other factors, they have produced a wider variety of lightning forecasts. One of these factors is the amount of ' graupel ' in clouds: These tiny soft bits of hail increase clouds' electrical charge. Another factor is air pollution. The dirtier the air, the more lightning. When Covid struck, for example, the reduction in air, road, and shipping traffic led to cleaner air, which slashed global lightning rates by about 15 percent. In 2022, changes to shipping pollution regulations similarly caused a huge reduction in lightning strikes over shipping lanes. Because of all these complexities, along with the fact that climate models typically struggle with small-scale phenomena like thunderstorms, lightning forecasts frequently disagree. Some even predict that global lightning might decrease, not increase. There is 'a large knowledge gap in the prediction of future global lightning activity,' says Yuzhong Zhang, an atmospheric chemist at Westlake University in Hangzhou, China. The World Wide Lightning Location Network records between 600,000 and 800,000 lightning strikes every day around the globe, or more than 200 million per year. This network, which has been running since 2004, picks up very-low-frequency radio waves created by lightning, which bounce off the ionosphere and travel around the globe. By detecting this signal at a handful of the dozens of global stations, and timing them to within nanoseconds, researchers can triangulate where and when lightning struck. The WWLLN (pronounced 'woollen') catches only about 30 percent of global lightning, missing a lot of little strikes but detecting 80 percent of high-energy strikes. Other local or commercial networks catch more strikes, but WWLLN has the longest and most consistent global dataset available to researchers. Jed Kaplan, an earth system scientist at the University of Calgary who combs through the WWLLN data each year, says that as of 2022 there were no clear trends in the global lightning data — though more recent data, he says, suggest a hint of an overall increase. In the Arctic, however, there are more solid signs. Holzworth's 2021 study of WWLLN data found that from 2010 to 2020, warmer summers saw more lightning hitting above the 65th parallel (around the middle of Alaska). The hottest year in this stretch, 2019 (which was globally 0.93 degrees Celsius warmer than the 1951-1980 average), saw three times more lightning in the Arctic as a fraction of the global total than the coolest year, 2011 (which was 0.65 degrees Celsius warmer). In other words, a 0.3-degree Celsius bump in global temperature came with a tripling of Arctic lightning. That's just for one 10-year stretch, cautions Holzworth, and it isn't clear that this trend will continue. In fact, he says, his as-yet-unpublished analysis suggests that lightning has dipped a bit in the Arctic in the last few years. Yet the Finnish weather company Vaisala, which runs its own lightning detection network, has seen an even more dramatic spike in the Far North. Its 2022 report says that while lightning strike numbers have remained steady up to the 65th parallel, researchers saw in 2021 nearly twice as many lightning events (including both lightning within clouds and lightning that strikes the ground) north of the 80th parallel than in the previous nine years combined. More lightning doesn't always lead to more fires, notes Kaplan. Fires require not just an ignition but also a lot of dry fuel to burn. The vast majority of lightning strikes in the tropics, but it comes with heavy rains that prevent fire. In some places, including in the United States, the majority of wildfires are started by human carelessness or equipment malfunctions, not by lightning. But in high latitudes, lightning is the main cause of large fires, so an increase in lightning activity in the north is cause for concern. The Alaska Fire Science Consortium is tracking what's going on in Alaska. The peak fire activity there occurs in June, as long, sunny days dry out 'duff fuels' — decomposing litter, lichen, and moss — and lightning storms hit more frequently. Those conditions stretch into July. By the end of July, Alaska tends to get more rain, dampening fires. The consortium's 2025 report notes that Alaska is getting warmer — the summer average is now more than 54 degrees F, compared to about 52 degrees F in 1970. It's getting wetter too, but not, for now, fast enough to offset the effects of warming on fire. And lightning is increasing: There has been a doubling in lightning strikes in Alaska's western interior over the past 10 years. 'We know that from the networks, but also from local people — not just the elders but middle-aged people — who have noticed things changing,' says Thoman. Much of Alaska has historically been too dry for lightning; now it is tipping over the edge to having just enough moisture in the air to form thunderstorms, Thoman says. All these factors have together led to more frequent large-fire years in Alaska. 'The big fire seasons are roughly doubling in frequency,' says Thoman. Lightning plays an important role in that. In 2015, for example, Alaska saw more than 50,000 strikes over a three-day period (more than a third of the state's annual average of 120,000 per summer), and it experienced its second largest fire season yet, with more than 5 million acres burned. Fire is a natural part of the northern ecosystem. But the new fire regime comes with hotter fires, says Thoman, which can incinerate rather than activate the seed cones of fire-adapted trees. Burning duff creates a huge amount of smoke, which is problematic for people who live downwind. And the burning of trees, which sometimes never grow back, can strip the landscape of shade and speed up permafrost melt, which releases methane — a powerful greenhouse gas. One recent study forecast that lightning strikes could more than double by 2100 in tundra and boreal forest areas that are underlain by permafrost. This, the authors write, could increase the area consumed by wildfire by more than five times and release large quantities of methane. Permafrost thaw isn't well represented in climate models, so the amount of greenhouse gas that might be released this way is unknown. 'There's not enough attention on this in my opinion,' says Thoman. There's one reason, though, to think that more lightning might help mitigate possible boosts in methane: by changing the chemistry of the atmosphere. In 2021, researchers flying planes over Colorado and Oklahoma to study the air during lightning storms were startled to find that strikes produced massive amounts of oxidants — more than 1,000 times the amount they were expecting to find. These oxidants — hydroxyl and the hydroperoxyl radical — are known to scrub away methane, acting like a kind of atmospheric cleanser. The effect can be dramatic, as Zhang and his colleagues learned by studying the reverse dynamic: a sharp increase in methane that occurred during Covid. The team calculated that the global decline in lightning — due to reduced traffic and air pollution during the pandemic — caused a dramatic 2 percent global reduction in hydroxyl in 2020, as compared to 2019. At the same time, atmospheric methane increased by about 15 parts per billion in 2020 — one of the biggest annual spikes ever seen and more than 50 percent greater than the rise in 2019. A host of different theories have been put forward to explain this methane boost, including industrial leaks and wetland emissions, but the lightning theory is powerful: Zhang estimates it could account for about half of the spike. For now, no one knows the likely magnitude of either effect. If lightning strikes continue to increase in the Arctic, or elsewhere, how much will that boost methane or mop it up? Thunderstorms, says Holzworth, play a hugely important role in moving ions and molecules around in the upper atmosphere, and the impacts of that activity on climate change are complex and unknown. 'These are pieces of the puzzle that need to be solved.' Holzworth thinks that in places where there's little lightning now, 'there will be more – maybe even in the Antarctic,' he says. 'But it's not so clear. The weather dynamics are changing.'
