WASHINGTON (AP) — Climate change has tripled the frequency of atmospheric wave events linked to extreme summer weather in the last 75 years and that may explain why long-range computer forecasts keep underestimating the surge in killer heat waves, droughts and floods, a new study says.
In the 1950s, Earth averaged about one extreme weather-inducing planetary wave event a summer, but now it is getting about three per summer, according to a study in Monday's Proceedings of the National Academy of Sciences. Planetary waves are connected to 2021's deadly and unprecedented Pacific Northwest heat wave, the 2010 Russian heatwave and Pakistan flooding and the 2003 killer European heatwave, the study said.
“If you’re trying to visualize the planetary waves in the northern hemisphere, the easiest way to visualize them is on the weather map to look at the waviness in the jet stream as depicted on the weather map,” said study co-author Michael Mann, a University of Pennsylvania climate scientist.
Planetary waves flow across Earth all the time, but sometimes they get amplified, becoming stronger, and the jet stream gets wavier with bigger hills and valleys, Mann said. It's called quasi-resonant amplification or QRA.
This essentially means the wave gets stuck for weeks on end, locked in place. As a result, some places get seemingly endless rain while others endure oppressive heat with no relief.
“A classic pattern would be like a high pressure out west (in the United States) and a low pressure back East and in summer 2018, that’s exactly what we had,” Mann said. “We had that configuration locked in place for like a month. So they (in the West) got the heat, the drought and the wildfires. We (in the East) got the excessive rainfall.”
“It's deep and it's persistent,” Mann said. “You accumulate the rain for days on end or the ground is getting baked for days on end.”
The study finds this is happening more often because of human-caused climate change, mostly from the burning of fossil fuels, specifically because the Arctic warms three to four times faster than the rest of the world. That means the temperature difference between the tropics and the Arctic is now much smaller than it used to be and that weakens the jet streams and the waves, making them more likely to get locked in place, Mann said.
“This study shines a light on yet another way human activities are disrupting the climate system that will come back to bite us all with more unprecedented and destructive summer weather events,” said Jennifer Francis, a climate scientist at the Woodwell Climate Research Center who wasn't involved in the research.
“Wave resonance does appear to be one reason for worsening summer extremes. On top of general warming and increased evaporation, it piles on an intermittent fluctuation in the jet stream that keeps weather systems from moving eastward as they normally would, making persistent heat, drought, and heavy rains more likely,” Francis said.
This is different than Francis' research on the jet stream and the polar vortex that induces winter extremes, said Mann.
There's also a natural connection. After an El Nino, a natural warming of the central Pacific that alters weather patterns worldwide, the next summer tends to be prone to more of these amplified QRA waves that become locked in place, Mann said. And since the summer of 2024 featured an El Nino, this summer will likely be more prone to this type of stuck jet stream, according to Mann.
While scientists have long predicted that as the world warms there will be more extremes, the increase has been much higher than what was expected, especially by computer model simulations, Mann and Francis said.
That's because the models “are not capturing this one vital mechanism,” Mann said.
Unless society stops pumping more greenhouse gases in the air, “we can expect multiple factors to worsen summer extremes,” Francis said. “Heat waves will last longer, grow larger and get hotter. Worsening droughts will destroy more agriculture.”
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FILE - A display at an Olympia Federal Savings branch shows a temperature of 107 degrees Fahrenheit, Monday, June 28, 2021, in the early evening in Olympia, Wash. (AP Photo/Ted S. Warren, File)
FILE - A sign in the window of the Dick's Drive-In posted due to excessive heat in Seattle's Capitol Hill neighborhood is shown Monday, June 28, 2021, in Seattle. (AP Photo/Ted S. Warren, File)
FILE - Survivors wade through water in their village Khairpur Nathan Shah, Pakistan, on Nov. 2, 2010, which is surrounded by floodwaters. (AP Photo/Shakil Adil, File)
DENVER (AP) — The Denver Broncos were slogging their way through a rare clunker Sunday against the Green Bay Packers when cornerback Pat Surtain II delivered the game-saving takeaway.
The reigning NFL defensive player of the year laid out for Jordan Love's deep throw to Christian Watson and secured his first interception of an injury-marred season, one that sparked the Broncos' playoff-clinching, come-from-behind 34-26 win Sunday.
“We may have to use him on offense some,” Bo Nix cracked.
Denver's second-year QB actually had plenty of firepower. Nix tied a career high with four touchdown passes — connecting with Michael Bandy, Courtland Sutton, Troy Franklin and Lil'Jordan Humphrey — to lead the Broncos (12-2) to their 11th consecutive victory.
The Broncos clinched a playoff berth and moved a game ahead of New England for the No. 1 seed in the AFC. They stayed two games ahead of the Los Angeles Chargers in the AFC West.
Green Bay lost star lost star pass rusher Micah Parsons, who went down with a non-contact knee injury while chasing down Nix. Parsons, who had energized the green and gold ever since his stunning trade from Dallas a week before the season opener, is believed to have suffered a torn ACL in his left knee, a person with knowledge of the injury told The Associated Press.
The person spoke on condition of anonymity because the severity of the injury hadn’t been confirmed by tests.
“I’m sickened,” Parsons, who forced a fumble on Denver's opening drive, told the AP in a text message.
Parsons’ injury is a devastating blow to the Packers (9-4-1), who fell a half-game behind the NFC North-leading Chicago Bears ahead of their Soldier Field showdown next weekend.
Parsons was steps away from a sack when he suddenly pulled up and fell to the ground, grabbing at his left knee.
The Packers also lost Watson to a chest injury after Surtain fell on him following his third-quarter interception. Green Bay coach Matt LaFleur confirmed that Watson went to a hospital for tests.
“I told the guys, ‘Nobody is going to feel sorry for us,’” LaFleur said. “Everybody’s going to have to elevate their play.”
The Packers opened the second half with a TD drive to take a 23-14 lead. After Denver went three-and-out, the Packers went for the kill shot with a deep throw to Watson on first down and Surtain came away with the ball, re-energizing both his sideline and the crowd.
“I think a play like that, a sudden turnover, just gets some adrenaline, gets some emotion back in the game,” said Nix, who capitalized on the takeaway by leading a touchdown drive that trimmed Denver's deficit to 23-21.
“He's had some ups and downs this season, he's battled through it, and that was a Pat Surtain play right there. None many can make it,” Nix said. “Big-time players make big plays in big moments.”
Riley Moss also recorded his first interceptions of the season. The Broncos sacked Love three times and held the Packers to just one touchdown in four trips into the red zone while going 4 for 4 themselves.
After scoring on their first five drives, the Packers managed one field goal in their final half-dozen possessions. The others ended in a pair of picks, two turnovers on downs and a punt.
“We got a lot of fight,” Surtain said. “The Packers, they got a great team on both sides of the ball. We knew it wasn't going to be easy. We kept reiterating that throughout the whole ball game: just finish, finish, finish and we'll get the job done. ... In order for us to be great, we've got to find a way to win those games.”
Surtain was one of several Broncos who comforted Parsons as the Packers' medical personnel attended to him on the field.
“It's very tough,” Surtain said. “Micah, he's a great player in this league and when you see a player of his caliber go down, we feel for him.”
The game featured a half-dozen lead changes.
“Well, we talked about it at halftime and we said that's the habitat we've been living in,” said Broncos coach Sean Payton, whose team has pulled out nine one-score victories during its 11-game winning streak, the franchise's longest since 2012.
“When you get comfortable operating in those games, you don't think anything of it,” Payton added.
Former Broncos kicker Brandon McManus kicked field goals of 56, 23 and 35 yards to help the Packers take a 16-14 halftime lead and added a 37-yarder in the fourth quarter that pulled Green Bay within 27-26 before the Broncos iced it on R.J. Harvey's 4-yard TD run.
Packers: In addition to Parsons and Watson, TE Josh Whyle (concussion) and RT Zach Tom (knee) got hurt.
Broncos: Harvey (ribs) was injured late in the game. Also, ILB Justin Strnad (right ankle) and S Brandon Jones (pectoral) got hurt and didn't return.
Packers. At Chicago on Saturday.
Broncos: Host Jacksonville next Sunday.
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Green Bay Packers' Christian Watson is hurt after Denver Broncos' Pat Surtain II intercepts a pass during the second half of an NFL football game Sunday, Dec. 14, 2025, in Denver. (AP Photo/Jack Dempsey)
Denver Broncos' Riley Moss celebrates an interception during the second half of an NFL football game against the Green Bay Packers Sunday, Dec. 14, 2025, in Denver. (AP Photo/Jack Dempsey)
Green Bay Packers' Keisean Nixon tries to stop Denver Broncos' Troy Franklin during the second half of an NFL football game Sunday, Dec. 14, 2025, in Denver. (AP Photo/David Zalubowski)
Denver Broncos' RJ Harvey celebrates his touchdown catch during the second half of an NFL football game against the Green Bay Packers Sunday, Dec. 14, 2025, in Denver. (AP Photo/David Zalubowski)
Green Bay Packers' Micah Parsons reacts after an injury during the second half of an NFL football game against the Denver Broncos Sunday, Dec. 14, 2025, in Denver. (AP Photo/Jack Dempsey)
Denver Broncos' Bo Nix scrambles during the first half of an NFL football game against the Green Bay Packers Sunday, Dec. 14, 2025, in Denver. (AP Photo/Jack Dempsey)
