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Japan Today
a day ago
- Science
- Japan Today
Study finds planetary waves linked to wild summer weather have tripled since 1950
By SETH BORENSTEIN 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 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.' © Copyright 2025 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.
Japan Today
28-05-2025
- Climate
- Japan Today
5-year forecast sees more killer heat, fires and temperature records
By SETH BORENSTEIN Get ready for several years of even more record-breaking heat that pushes Earth to more deadly, fiery and uncomfortable extremes, two of the world's top weather agencies forecast. There's an 80% chance the world will break another annual temperature record in the next five years, and it's even more probable that the world will again exceed the international temperature threshold set 10 years ago, according to a five-year forecast released Wednesday by the World Meteorological Organization and the UK Meteorological Office. 'Higher global mean temperatures may sound abstract, but it translates in real life to a higher chance of extreme weather: stronger hurricanes, stronger precipitation, droughts,' said Cornell University climate scientist Natalie Mahowald, who wasn't part of the calculations but said they made sense. 'So higher global mean temperatures translates to more lives lost.' With every tenth of a degree the world warms from human-caused climate change 'we will experience higher frequency and more extreme events (particularly heat waves but also droughts, floods, fires and human-reinforced hurricanes/typhoons),' emailed Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research in Germany. He was not part of the research. And for the first time there's a chance -- albeit slight -- that before the end of the decade, the world's annual temperature will shoot past the Paris climate accord goal of limiting warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) and hit a more alarming 2 degrees Celsius (3.6 degrees Fahrenheit) of heating since the mid-1800s, the two agencies said. There's an 86% chance that one of the next five years will pass 1.5 degrees and a 70% chance that the five years as a whole will average more than that global milestone, they figured. The projections come from more than 200 forecasts using computer simulations run by 10 global centers of scientists. Ten years ago, the same teams figured there was a similar remote chance — about 1% — that one of the upcoming years would exceed that critical 1.5 degree threshold and then it happened last year. This year, a 2-degree Celsius above pre-industrial year enters the equation in a similar manner, something UK Met Office longer term predictions chief Adam Scaife and science scientist Leon Hermanson called 'shocking.' 'It's not something anyone wants to see, but that's what the science is telling us,' Hermanson said. Two degrees of warming is the secondary threshold, the one considered less likely to break, set by the 2015 Paris agreement. Technically, even though 2024 was 1.5 degrees Celsius warmer than pre-industrial times, the Paris climate agreement's threshold is for a 20-year time period, so it has not been exceeded. Factoring in the past 10 years and forecasting the next 10 years, the world is now probably about 1.4 degrees Celsius (2.5 degrees Fahrenheit) hotter since the mid 1800s, World Meteorological Organization climate services director Chris Hewitt estimated. 'With the next five years forecast to be more than 1.5C warmer than preindustrial levels on average, this will put more people than ever at risk of severe heat waves, bringing more deaths and severe health impacts unless people can be better protected from the effects of heat. Also we can expect more severe wildfires as the hotter atmosphere dries out the landscape,' said Richard Betts, head of climate impacts research at the UK Met Office and a professor at the University of Exeter. Ice in the Arctic — which will continue to warm 3.5 times faster than the rest of the world — will melt and seas will rise faster, Hewitt said. What tends to happen is that global temperatures rise like riding on an escalator, with temporary and natural El Nino weather cycles acting like jumps up or down on that escalator, scientists said. But lately, after each jump from an El Nino, which adds warming to the globe, the planet doesn't go back down much, if at all. 'Record temperatures immediately become the new normal,' said Stanford University climate scientist Rob Jackson. © Copyright 2025 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.
