Earth

A flash flood surged down a river in India’s Himalayan Uttarakhand state on February 7, killing at least 30 people and washing away two hydroelectric power stations.
As rescue workers search for more than 100 people who are still missing, officials and scientists are trying to unravel the causes of the sudden flood. Did a glacier high up in the mountains collapse, releasing a huge plug of frigid meltwater that spilled into the river? Or was the culprit a landslide that then triggered an avalanche? And what, if any, link might these events have to a changing climate?
Here are three things to know about what might have caused the disaster in Uttarakhand.
1. One possible culprit was the sudden break of a glacier high in the mountains.
News reports in the immediate wake of the disaster suggested that the floodwaters were caused by the sudden overflow of a glacial lake high up in the mountain, an event called a glacial lake outburst flood.
“It’s likely too early to know what exactly happened,” says Anjal Prakash, the research director of the Bharti Institute of Public Policy at the Indian School of Business in Hyderabad. Satellite images show that a section of a glacier broke off, but how that break relates to the subsequent floods is still unknown. One possibility is that the glacier was holding back a lake of meltwater, and that heavy snowfall in the region two days earlier added enough volume to the lake that the water forced its way out, breaking the glacier and surging into nearby rivers.
This scenario is certainly in line with known hazards for the region. “These mountains are very fragile,” says Prakash, who was also a lead author on the Intergovernmental Panel on Climate Change’s 2019 special report on oceans and the cryosphere, Earth’s icy places. But, he notes, there isn’t yet much on-the-ground data to help clarify events. “The efforts are still focused on relief at the moment.”
2. A landslide may be to blame instead.
Other researchers contend that the disaster wasn’t caused by a glacial lake outburst flood at all. Instead, says Daniel Shugar, a geomorphologist at the University of Calgary in Canada, satellite images snapped during the disaster show the telltale marks of a landslide: a dark scar snaking through the white snow and clouds of dust clogging the air above. “You could see this train of dust in the valley, and that’s common for a very large landslide,” Shugar says.
“WOW,” he wrote on Twitter the morning of February 7, posting side-by-side satellite shots of a dark area of possible “massive dust deposition,” contrasted against the same snowy, pristine region just the day before.

Landslides — the sudden failure of a slope, sending a rush of rocks and sediment downhill — can be triggered by anything from an earthquake to an intense deluge of rain. In high, snowy mountains, cycles of freezing and thawing and refreezing again can also begin to break the ground apart; the ice-filled cracks can slowly widen over time, setting the stage for sudden failure, and then, disaster.
The satellite images seem to point clearly to such a landslide, rather than a typical glacial lake overflow, Shugar says. The force of the landslide may have actually broken off that piece of hanging glacier, he says. Another line of evidence against a sudden lake burst is that “there were no lakes of any size visible” in the satellite images taken over the region.
However, an outlying question for this hypothesis is where the floodwaters came from. It might be that one of the rivers draining down the mountain was briefly dammed by the rockfall; a sudden release of that dam could send a large plug of water from the river swiftly and disastrously downhill. “But that’s a pure guess at the moment,” Shugar says.
3. It’s not yet clear whether climate change played a role in the disaster.
The risk of both glacial lake outburst floods and freeze-thaw-related landslides in Asia’s high mountains has increased due to climate change. At first glance, “it was a climate event,” Prakash says. “But the data are still coming.”
The region, which includes the Hindu Kush Himalayan mountains and the Tibetan Plateau, “has been a climate change hot spot for a pretty long time,” Prakash says. The region is often called Earth’s third pole, because the stores of ice and snow in the Himalayan watershed amount to the largest reserves of freshwater outside of the polar regions. The region is the source of 10 major river systems that provide water to almost 2 billion people.
Climate change reports have warned that warming is not only threatening this water supply, but also increasing the likelihood of natural hazards (SN: 5/29/19). In the Intergovernmental Panel on Climate Change’s 2019 special report on oceans and the cryosphere, scientists noted that glacier retreat, melting snow and thawing permafrost are making mountain slopes more unstable and also increasing the number of glacial lakes, upping the likelihood of a sudden, catastrophic failure (SN: 9/25/19).
A 2019 comprehensive assessment focusing on climate change’s impacts in Asia’s high mountains found that the glaciers in the region have retreated much more quickly in the last decade than was anticipated, Prakash says, “and that is alarming for us.” Here’s another way to look at it: Glaciers are retreating twice as fast as they were at the end of the 20th century (SN: 6/19/19).
Glacier-related landslides in the region have also become increasingly common in the last decade, as the region warms and destabilizing freeze-thaw cycles within the ground occur higher and higher up on the slopes.
But in the case of this particular disaster, Shugar says, it’s just hard to say conclusively at this point what role climate change might have played, or even what specific event might have triggered a landslide. “Sometimes there is no trigger; sometimes it’s just time,” he says. “Or it’s that we just don’t understand the trigger.”

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Pandemic-related shutdowns may have spared Earth’s atmosphere some greenhouse gas emissions last year, but the world continued to warm.
Water temperature measurements from around the globe indicate that the total amount of heat stored in the upper oceans in 2020 was higher than any other year on record dating back to 1955, researchers report online January 13 in Advances in Atmospheric Sciences. Tracking ocean temperature is important because warmer water melts more ice off the edges of Greenland and Antarctica, which raises sea levels (SN: 4/30/20) and supercharges tropical storms (SN: 11/11/20).
Researchers estimated the total heat energy stored in the upper 2,000 meters of Earth’s oceans using temperature data from moored sensors, drifting probes called Argo floats, underwater robots and other instruments (SN: 5/19/10). The team found that upper ocean waters contained 234 sextillion, or 1021, joules more heat energy in 2020 than the annual average from 1981 to 2010. Heat energy storage was up about 20 sextillion joules from 2019 — suggesting that in 2020, Earth’s oceans absorbed about enough heat to boil 1.3 billion kettles of water.
This analysis may overestimate how much the oceans warmed last year, says study coauthor Kevin Trenberth, a climate scientist with the U.S. National Center for Atmospheric Research who is currently based in Auckland, New Zealand. So the researchers also crunched ocean temperature data using a second, more conservative method for estimating total annual ocean heat and found that the jump from 2019 to 2020 could be as low as 1 sextillion joules. That’s still 65 million kettles brought to boil.
The three other warmest years on record for the world’s oceans were 2017, 2018 and 2019. “What we’re seeing here is a variant on the movie Groundhog Day,” says study coauthor Michael Mann, a climate scientist at Penn State. “Groundhog Day has a happy ending. This won’t if we don’t act now to dramatically reduce carbon emissions.” More

In August, a massive wildfire tore through the San Lorenzo Valley north of Santa Cruz, Calif., destroying almost 1,500 structures and exposing many others to extreme heat. Before the fire was even out, lab tests revealed benzene levels as high as 9.1 parts per billion in residential water samples — nine times higher than the state’s maximum safety level.
This isn’t the first time the carcinogen has followed wildfires: California water managers found unsafe levels of benzene and other volatile organic compounds, or VOCs, in Santa Rosa after the Tubbs Fire in 2017, and in Paradise after the Camp Fire in 2018.
Scientists suspected that, among other possibilities, plastic drinking water pipes exposed to extreme heat released the chemicals (SN: 11/13/20). Now, lab experiments show that’s possible.  
Andrew Whelton, an environmental engineer at Purdue University in West Lafayette, Ind., and colleagues subjected commonly available pipes to temperatures from 200° Celsius to 400° C. Those temperatures, hot enough to damage but not destroy pipes, can occur as heat radiates from nearby flames, Whelton says.
A plastic water pipe (left) and meter box (right) recovered from homes in Paradise, Calif., after the Camp Fire scorched the community in 2018 reveal the degree to which plastics can melt when exposed to high temperatures.Andrew Whelton/Purdue University (CC-BY-ND)
When the researchers then submerged the pipes in water and cooled them, varying amounts of benzene and VOCs — more than 100 chemicals in some tests — leached from 10 of the 11 types of pipe into the water, the team reports December 14 in Environmental Science: Water Research & Technology.
“Some contamination for the past fires likely originated from thermally damaged plastics,” says Whelton. It’s impossible to do experiments in the midst of a raging fire to pinpoint the exact source of the contamination, he says, but inspecting damaged pipes after the fact can suggest what temperatures they may have experienced.
Benzene exposure can cause immediate health problems, including skin and throat irritation, dizziness, and longer-term effects such as leukemia. The team suggests testing drinking water if fire comes anywhere near your property and, if possible, replacing any plastic in a home’s water system with heat-resistant metal. More

A massive plume of smoke lofted into the stratosphere during Australia’s fires may represent a new class of “volcanic-scale” pyrocumulonimbus clouds. More

Fifteen years of grading warming’s impact on the Arctic has made one thing abundantly clear: Climate change has drastically altered the Arctic in that short time period.
Breaking unfortunate records is “like whack-a-mole,” says Jackie Richter-Menge, a climate scientist at the University of Alaska Fairbanks and an editor of the 2020 Arctic Report Card, released December 8 at the virtual meeting of the American Geophysical Union. From sea ice lows to temperature highs, records keep popping up all over the place. For instance, in June, a record-high 38° Celsius (100.4° Fahrenheit) temperature was recorded in the Arctic Circle (SN:6/23/20). And in 2018, winter ice on the Bering Sea shrank to a 5,500 year low (SN:9/3/20).
“But quite honestly, the biggest headline is the persistence and robustness of the warming,” Richter-Menge says. In 2007, only a year after the first Arctic Report Card, summer sea ice reached a record low, shrinking to an area 1.6 million square kilometers smaller than the previous year. Then, only five years later, the report card noted a new low, 18 percent below 2007. In 2020, sea ice didn’t set a record but not for lack of trying: It still was the second lowest on record in the last 42 years.  
“The transformation of the Arctic to a warmer, less frozen and biologically changed region is well under way,” the report concludes. And it’s changing faster than expected when researchers launched the report card in 2006. The annual average air temperature in the Arctic is rising two to three times faster than the rest of the globe, Richter-Menge says. Over the last 20 years, it’s warmed at a rate of 0.77 degrees C per decade, compared with the global average of 0.29 degrees C per decade.

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Improvements in research techniques over the last 15 years have helped researchers more thoroughly observe warming’s impact and how different aspects of Arctic climate change are linked to one another, she says. These improvements include the ability to measure ice mass via gravity measurements taken by the Gravity Recovery and Climate Experiment (GRACE) satellite. Other satellites have provided additional observations from above while on-the-ground measurements, such as by the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), have provided up-close sea ice measurements (SN:4/8/20). The report has also begun to include on-the-ground observations of the Arctic’s Indigenous people, who experiences these changes directly (SN:12/11/19).
The changes have revealed few bright spots but one is the rebound of bowhead whales, which were hunted almost to extinction around the turn of the 20th century. While researchers are careful to note that the whales are still vulnerable, the four populations of the whales (Balaena mysticetus) now range from 218 in the Okhotsk Sea to around 16,800 in the Bering, Chukchi and Beaufort seas. Researchers suggest that the whales’ rebound is due, at least in part, to the warming that has occurred over the last 30 years. Earlier sea ice melting and warmer surface water means more krill and other food for these baleen feeders.
In a rare bit of good news from the Arctic, researchers report that bowhead whales are on the rebound. Unfortunately, the same warming that has aided the whales has melted ice sheets and increased hardships for Indigenous hunters.Nature Picture Library/Alamy Stock Photo
But don’t be fooled. The potential good news is overshadowed by the bad news. There’s been “this accumulation of knowledge and insights that we’ve gained over 15 years,” says Mark Serreze, a climate scientist at the National Snow and Ice Data Center in Boulder, Colo., who wasn’t involved in this year’s report. The 2020 research is “an exclamation point on the changes that have been unfolding,” he says. “The bowhead whales are doing OK, but that’s about it.” More

It’s official: 2020 now has the most named storms ever recorded in the Atlantic in a single year.
On November 9, a tropical disturbance brewing in the northeastern Atlantic Ocean gained enough strength to become a subtropical storm. With that, Theta became the year’s 29th named storm, topping the 28 that formed in 2005.
With maximum sustained winds near 110 kilometers per hour as of November 10, Theta is expected to churn over the open ocean for several days. It’s too early to predict Theta’s ultimate strength and trajectory, but forecasters with the National Oceanic and Atmospheric Administration say they expect the storm to weaken later in the week.
If so, like most of the storms this year, Theta likely won’t become a major hurricane. That track record might be the most surprising thing about this season — there’s been a record-breaking number of storms, but overall they’ve been relatively weak. Only five — Laura, Teddy, Delta, Epsilon and Eta — have become major hurricanes with winds topping 178 kilometers per hour, although only Laura and Eta made landfall near the peak of their strength as Category 4 storms.

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Even so, the 2020 hurricane season started fast, with the first nine storms arriving earlier than ever before (SN: 9/7/20). And the season has turned out to be the most active since naming began in 1953, thanks to warmer-than-usual water in the Atlantic and the arrival of La Niña, a regularly-occurring period of cooling in the Pacific, which affects winds in the Atlantic and helps hurricanes form (SN: 9/21/19). If a swirling storm reaches wind speeds of 63 kilometers per hour, it gets a name from a list of 21 predetermined names. When that list runs out, the storm gets a Greek letter.
While the wind patterns and warm Atlantic water temperatures set the stage for the string of storms, it’s unclear if climate change is playing a role in the number of storms. As the climate warms, though, you would expect to see more of the destructive, high-category storms, says Kerry Emanuel, an atmospheric scientist at MIT. “And this year is not a poster child for that.” So far, no storm in 2020 has been stronger than a Category 4. The 2005 season had multiple Category 5 storms, including Hurricane Katrina (SN: 12/20/05).
There’s a lot amount of energy in the ocean and atmosphere this year, including the unusually warm water, says Emanuel. “The fuel supply could make a much stronger storm than we’ve seen,” says Emanuel, “so the question is: What prevents a lot of storms from living up to their potential?”
On September 14, five named storms (from left to right, Sally, Paulette, Rene, Teddy and Vicky) swirled in the Atlantic simultaneously. The last time the Atlantic held five at once was 1971.NOAA
A major factor is wind shear, a change in the speed or direction of wind at different altitudes. Wind shear “doesn’t seem to have stopped a lot of storms from forming this year,” Emanuel says, “but it inhibits them from getting too intense.” Hurricanes can also create their own wind shear, so when multiple hurricanes form in close proximity, they can weaken each other, Emanuel says. And at times this year, several storms did occupy the Atlantic simultaneously — on September 14, five storms swirled at once.
It’s not clear if seeing hurricane season run into the Greek alphabet is a “new normal,” says Emanuel. The historical record, especially before the 1950s is spotty, he says, so it’s hard to put this year’s record-setting season into context. It’s possible that there were just as many storms before naming began in the ‘50s, but that only the big, destructive ones were recorded or noticed. Now, of course, forecasters have the technology to detect all of them, “so I wouldn’t get too bent out of shape about this season,” Emanuel says.
Some experts are hesitant to even use the term “new normal.”
“People talk about the ‘new normal,’ and I don’t think that is a good phrase,” says James Done, an atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colo. “It implies some new stable state. We’re certainly not in a stable state — things are always changing.” More

August 2020 has been a devastating month across large swaths of the United States: As powerful Hurricane Laura barreled into the U.S. Gulf Coast on August 27, fires continued to blaze in California. Meanwhile, farmers are still assessing widespread damage to crops in the Midwest following an Aug. 10 “derecho,” a sudden, hurricane-force windstorm.
Each of these extreme weather events was the result of a particular set of atmospheric — and in the case of Laura, oceanic — conditions. In part, it’s just bad luck that the United States is being slammed with these events back-to-back-to-back. But for some of these events, such as intense hurricanes and more frequent wildfires, scientists have long warned that climate change has been setting the stage for disaster.
Science News takes a closer look at what causes these kinds of extreme weather events, and the extent to which human-caused climate change may be playing a role in each of them.
On August 25, NASA’s GOES-West satellite watched as hazy gray smoke emanating from hundreds of wildfires in California drifted eastward, while Hurricane Laura barreled toward Louisiana and Texas. Farther south and east are the wispy remnants of Tropical Storm Marco. Laura made landfall on August 27 as a Category 4 hurricane.NOAA
California wildfires
A “dry lightning” storm, which produced nearly 11,000 bursts of lightning between August 15 and August 19, set off devastating wildfires in across California. To date, these fires have burned more than 520,000 hectares.
That is “an unbelievable number to say out loud, even in the last few years,” says climate scientist Daniel Swain, of the Institute of the Environment and Sustainability at UCLA.
Lightning crackles over Mitchell’s Cove in Santa Cruz, Calif., on August 16, part of a rare and severe storm system that triggered wildfires across the state.Shmuel Thaler/The Santa Cruz Sentinel via AP
The storm itself was the result of a particular, unusual set of circumstances. But the region was already primed for fires, the stage set by a prolonged and record-breaking heat wave in the western United States — including one of the hottest temperatures ever measured on Earth, at Death Valley, Calif. — as well as extreme dryness in the region (SN: 8/17/20). And those conditions bear the fingerprints of climate change, Swain says.
The extreme dryness is particularly key, he adds. “It’s not just incremental; it absolutely matters how dry it is. You don’t just flip a switch from dry enough to burn to not dry enough to burn. There’s a wide gradient up to dry enough to burn explosively.”
Both California’s average heat and dryness have become more severe due to climate change, dramatically increasing the likelihood of extreme wildfires. In an Aug. 20 study in Environmental Research Letters, Swain and colleagues noted that over the last 40 years, average autumn temperatures increased across the state by about 1 degree Celsius, and statewide precipitation dropped by about 30 percent. That, in turn, has more than doubled the number of autumn days with extreme fire weather conditions since the early 1980s, they found.
An unusual dry lightning storm combined with very dry vegetation and a record-breaking heat wave to spark hundreds of wildfires across California between August 15 and August 19. One group of these fires, collectively referred to as the LNU Lightning Complex, blazed through Napa, Sonoma, Solano, Yolo and Lake counties. Firefighters continued to battle the LNU complex fires on August 23, including in unincorporated Lake County, Calif. (shown).AP Photo/Noah Berger
Although fall fires in California tend to be more wind-driven, and summertime fires more heat-driven, studies show that the fingerprint of climate change is present in both, Swain says. “A lot of it is very consistent with the long-term picture that scientists were suggesting would evolve.”
Though the stage had been set by the climate, the particular trigger for the latest fires was a “dry lightning” storm that resulted from a strange confluence of two key conditions, each in itself rare for the region and time of year. “’Freak storm’ would not be too far off,” Swain says.
Smoke still engulfed California on August 24, as more than 650 wildfires continued to blaze across the state (red dots indicate likely fire areas). The two largest fires, both in Northern California, were named for the lightning storm that sparked them: the LNU Lightning Complex and the SCU Lightning Complex. They are now second and third on the list of California’s largest wildfires.NASA Worldview, Earth Observing System Data and Information System (EOSDIS)
The first was a plume of moisture from Tropical Storm Fausto, far to the south, which managed to travel north to California on the wind and provide just enough moisture to form clouds. The second was a small atmospheric ripple, the remnants of an old thunderstorm complex in the Sonoran Desert. That ripple, Swain says, was just enough to kick-start mixing in the atmosphere; such vertical motion is the key to thunderstorms. The resulting clouds were stormy but very high, their bases at least 3,000 meters aboveground. They produced plenty of lightning, but most rain would have evaporated during the long dry journey down.
Possible links between climate change and the conditions that led to such a dry lightning storm would be “very hard to disentangle,” Swain says. “The conditions are rare to begin with, and not well modeled from a weather perspective.”
But, he adds, “we know there’s a climate signal in the background conditions that allowed that rare event to have the outcome it did.”
Midwest derecho
On August 10, a powerful windstorm with the ferocity of a hurricane traveled over 1,200 kilometers in just 14 hours, leaving a path of destruction from eastern South Dakota to western Ohio.
The storm was what’s known as a derecho, roughly translating to “straight ahead.” These storms have winds rivaling the strength of a hurricane or tornado, but push forward in one direction instead of rotating. By definition, a derecho produces sustained winds of at least 93 kilometers per hour (similar to the fury of tropical storm-force winds), nearly continuously, for at least 400 kilometers. Their power is equally devastating: The August derecho flattened millions of hectares of crops, uprooted trees, damaged homes, flipped trucks and left hundreds of thousands of people without power.
A powerful derecho on August 10 twisted these corn and soybean grain bins in Luther, Iowa. The storm-force winds swept 1,200 kilometers across the U.S. Midwest, from South Dakota to Ohio, damaging homes and croplands and leaving hundreds of thousands of people without power.Daniel Acker/Getty Images
The Midwest has had many derechos before, says Alan Czarnetzki, a meteorologist at the University of Northern Iowa in Cedar Falls. What made this one significant and unusual was its intensity and scale — and, Czarnetzki notes, the fact that it took even researchers by surprise.
Derechos originate within a mesoscale convective system — a vast, organized system of thunderclouds that are the basic building block for many different kinds of storms, including hurricanes and tornadoes. Unlike the better-known rotating supercells, however, derechos form from long bands of swiftly moving thunderstorms, sometimes called squall lines. In hindsight, derechos are easy to recognize. In addition to the length and strength conditions, derechos acquire a distinctive bowlike shape on radar images; this one appeared as though the storm was aiming its arrow eastward.
But the storms are much more difficult to forecast, because the conditions that can lead them to form can be very subtle. And there’s overall less research on these storms than on their more dramatic cousins, tornadoes. “We have to rely on situational awareness,” Czarnetzki says. “Like people, sometimes you can have an exceptional storm arise from very humble origins.”

The Aug. 10 derecho was particularly long and strong, with sustained winds in some places of up to 160 kilometers per hour (100 miles an hour). Still, such a strong derecho is not unheard of, Czarnetzki says. “It’s probably every 10 years you’d see something this strong.”
Whether such strong derechos might become more, or less, common due to climate change is difficult to say, however. Some anticipated effects of climate change, such as warming at the planet’s surface, could increase the likelihood of more and stronger derechos by increasing atmospheric instability. But warming higher in the atmosphere, also a possible result of climate change, could similarly increase atmospheric stability, Czarnetzki says. “It’s a straightforward question with an uncertain answer.”
Atlantic hurricanes
Hurricane Laura roared ashore in Louisiana in the early morning hours of August 27 as a Category 4 hurricane, with sustained winds of about 240 kilometers per hour (150 miles per hour). Just two days earlier, the storm had been a Category 1. But in the mere 24 hours from August 25 to August 26, the storm rapidly intensified, supercharged by warm waters in the Gulf of Mexico.
Hurricane Laura intensified rapidly due to the warm waters of the Gulf of Mexico, strengthening from a Category 1 hurricane on August 25 to a Category 4 on August 26 (shown). The U.S. National Hurricane Center warned coastal residents of Louisiana and Texas to expect a storm surge — ocean waters elevated by the storm above the normal tide level — of as much as five meters.NOAA
The Atlantic hurricane season is already setting several new records, with the National Oceanographic and Atmospheric Administration predicting as many as 25 named storms, the most the agency has ever anticipated (SN: 8/7/20).
At present, 2005 still holds the record for the most named storms to actually form in the Atlantic in a given season, at 28 (SN: 8/22/18). But 2020 may yet surpass that record. By August 26, 13 named storms had already formed in the Atlantic, the most ever before September.
The previous week, researchers pondered whether another highly unusual set of circumstances might be in the offing. As Laura’s track shifted southward, away from Florida, tropical storm Marco appeared to be on track to enter the Gulf of Mexico right behind it. That might have induced a type of physical interaction known as a Fujiwhara effect, in which a strong storm might strengthen further as it absorbs the energy of a lesser storm. In perhaps a stroke of good luck in the midst of this string of weather extremes, Marco dissipated instead.
As Hurricane Laura approached landfall, the U.S. National Hurricane Center warned that “unsurvivable” storm surges of up to five meters could inundate the Gulf Coast in parts of Texas and Louisiana. Storm surge is the height to which the seawater level rises as a result of a storm, on top of the normal tidal level.
Debris litters Lake Charles, La., in the aftermath of Hurricane Laura’s landfall August 27.AP Photo/Gerald Herbert
It’s impossible to attribute the fury of any one storm to climate change, but scientists have observed a statistically significant link between warmer waters and hurricane intensity. Warm waters in the Atlantic Ocean, the result of climate change, juiced up 2017’s hurricanes, including Irma and Maria, researchers have found (SN: 9/28/18).
And the Gulf of Mexico’s bathlike waters have notably supercharged several hurricanes in recent years. In 2018, for example, Hurricane Michael intensified rapidly before slamming into the Florida panhandle (SN: 10/10/18). And in 2005, hurricanes Katrina and Rita did the same before making landfall (SN: 9/13/05).
As for Laura, one contributing factor to its rapid intensification was a drop in wind shear as it spun through the Gulf.  Wind shear, a change in the speed and/or direction of winds with height, can disrupt a storm’s structure, robbing it of some of its power.  But the Gulf’s warmer-than-average waters, which in some locations approached 32.2° C (90° Fahrenheit), were also key to the storm’s sudden strength. And, by warming the oceans, climate change is also setting the stage for supercharged storms, scientists say. 

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