From London to Shanghai, many parts of the world have been gripped by unprecedented heat in recent weeks. In June, Tokyo saw nine consecutive days above 35ºC, the worst heat wave since official records began in the 1870s. In mid-July, the UK broke records as temperatures climbed above 40ºC for the first time since records began. Meanwhile, forest fires ravaged parts of France, Spain, Greece and Germany. And China has faced several large-scale heat waves, including one that affected more than 400 cities last week.
Climatologists have long warned that heat waves will strike more often and at higher temperatures as the world warms. However, according to research published last month1, the future has arrived faster than researchers feared, especially in Western Europe, which is a hot spot for heat waves. It’s not just increasingly intense heat waves  they’re record-breaking heat waves that have exceeded expectations derived from climate models.
Scientists are now trying to dissect the details of this year’s heat waves to better understand how extreme heat will affect society in the future.”The scientific community has clearly been thinking about the possibility of these events,” says Eunice Lo, a climate scientist at the University of Bristol in the UK who studied the heat wave in the UK. But “it was still quite surreal that it actually happened”.
Deadly heat
Extreme heat is one of the deadliest consequences of global warming. It kills people directly, such as those who work outside. And it overloads power grids, cutting off electricity at a time when people most need air conditioning or fans to survive in overheated homes. A heat wave in Europe in 2003 is estimated to have killed more than 70,000 people. And heat waves can also exacerbate other disasters, such as wildfires, and take a heavy toll on mental health. Although heat waves have worsened over the past few years, studies of the most extreme examples jumped ahead after the June 2021 heat wave in the Pacific Northwest region of North America.
This heatwave was so far that it essentially reset the field of extreme heat research, says Vikki Thompson, a climatologist from Bristol. In a study published in May, she and her colleagues showed that only five heat waves recorded anywhere in the world since 1960 were more extreme, as measured by the deviation from the previous decade’s climate. Just looking at temperature records in the Pacific Northwest from years before the event, it seemed “quite unlikely” that such a record-breaking heat wave could happen, he says. And yet it happened driven mainly by a high-pressure atmospheric system that flowed in hot air, combined with drier-than-normal soil conditions across much of the region.
Defying expectations
This year’s July heatwave in the UK was not as severe, but it could still go down in history as the event that jolted the nation into awareness of the dangers of extreme heat. On 18 and 19 July, a large part of the country set new temperature records, in many cases as much as 3 or 4 ºC higher than previous ones (see “Warm extremes”). Forty-six weather stations beat the country’s previous record temperature of 38.7ºC, set just three years ago. Hundreds of people are estimated to have died. To some extent, scientists predicted this. A climate modeling study published two years ago found it possible, though not likely, for the UK to exceed 40ºC3 in the coming decades. And yet it did this year, with a new national high of 40.3ºC.
The fact that temperatures exceeded the threshold much faster than expected may stem from the fact that climate models do not capture everything that affects heat waves and therefore do not project future extreme temperatures quite accurately. Changes in factors, including land use and irrigation, affect heat waves in ways that are not yet fully accounted for in models. This means that model projections can sometimes incorrectly estimate the true impact of climate change.
An analysis by the international research group World Weather Attribution on 28 July found that man-made climate change made this year’s UK heatwave at least ten times more likely. The study also concluded that without global warming, the heat wave would have been 2-4ºC cooler. “It’s further evidence that there are some things we’re unlikely to capture with the models,” says Peter Stott, a climate scientist at the Met Office, the UK’s national weather service in Exeter, who co-authored the 2020 UK study. “There is a research question.
Dynamic change
Apart from the UK, much of Europe has already experienced several heatwaves this year. In fact, the continent has seen record-breaking heat several times over the past five years, says Kai Kornhuber, a climate scientist at Columbia University in New York. He was part of the team that identified Western Europe as particularly vulnerable to heat waves. Over the past four decades, extreme heat there has increased three to four times faster than in other mid-latitude regions of the Northern Hemisphere.
This could be because the atmospheric jet stream, which flows eastward across the North Atlantic Ocean, often splits into two separate strands as it approaches Europe. When this happens, the filaments can lead storms away from Europe and allow heat waves to develop and persist. It’s not yet clear whether climate change is leading to more of these “double jets,” but the pattern sparked this July’s heat wave in Western Europe and is responsible for many other recent heat events there.Similar patterns of atmospheric dynamics may prove important in revealing the factors that make heat events even more extreme than expected, Kornhuber says.
Synchronized waves
Another notable feature of the last few months is that extreme heat has occurred simultaneously in several parts of the world (see “In Red”). China and western North America basked in warmer than normal temperatures in late July, at the same time as Europe. Such concurrent heat waves became six times more common in the Northern Hemisphere between 1979 and 2019, a study published in February found.
One reason may be atmospheric patterns called Rossby waves, which settle into a serpentine shape around the entire planet, creating stagnant weather patterns in certain locations that then become prone to extreme heat. These may or may not become more common with global warming. But the overall chance of current heat waves unrelated to atmospheric patterns is increasing as the climate warms, says Deepti Singh, a climatologist at Washington State University in Vancouver. “The whole world is warming, and it’s only increasing the likelihood that there will be regions of extreme heat,” he says.
Heatwaves are also coming earlier in the year in some places, such as India and Pakistan, which experienced baking temperatures from March to May. Parts of India topped 44ºC in late March, well ahead of the usual hottest part of the year. At least 90 people died. The World Weather Attribution Group found that a heat wave was 30 times more likely due to climate change. As global temperatures continue to rise, climate scientists are re-emphasizing the importance of reducing carbon emissions and increasing people’s ability to adapt to extreme temperatures. The UK heatwave was a major wake-up call about the country’s vulnerability to extreme heat, says Stott. After decades of working on climate projections for the future, he was most horrified to see wildfires raging in London’s urban area, fueled by extreme heat. “It was very sobering, really, and shocking that it happened.
Source Reference: https://www.nature.com/articles/d41586-022-02114-y
that’s all beause of global warming 💯