Jet stream buckles as heat increases, causing more heatwaves

Boston — The heat rolled in, the lights went out, a fire tornado materialised in the sky and the hottest temperature anywhere in the world since 1931 was recorded in Death Valley.

It was a California weekend for the history books, adding to 2020’s global tally of extremes — including fires, heatwaves and tropical storms. This year has arguably offered a glimpse into the future of our climate-changed world.

But as far as the Golden State is concerned, that future may be here — now.

“These are things we have in the projections for mid-century, not 2020,” said Nik Steinberg, head of research at Moody’s Four Twenty Seven, an analytics company that provides climate-risk assessments for business and government. “They are becoming part of the norm and happening much quicker than anticipated.”

The first seven months of 2020 were the second warmest on record going back some 141 years, according to the US National Centres for Environmental Information. In April, Florida baked under summer-like temperatures; Siberia has been setting heat records all summer; and the US southwest has sweltered under a high pressure system that’s kept the region’s annual monsoon at bay.

It’s this large heat dome — stuck like a big rock in a stream — that’s allowed temperatures to break records across California. A resulting energy spike tied to air conditioning triggered the subsequent blackouts that have left millions without power.

It used to be that these heat domes would move on after a few days. But as the world warms, they can sometimes become stuck. And the longer they stay stuck, the more destructive they can become. These weather patterns are likely to be more common as the jet stream, the river of air that circles the globe, becomes weaker.

Why is it weakening? The difference between summer temperatures at the equator and the North Pole is shrinking, causing the jet stream to lose some of its power. That can lead to buckles in its flow that make it harder for cooler, lower pressure systems to muscle their way in and bring relief. In recent years, people trapped beneath high pressure systems have faced elongated heatwaves, while those under low pressure systems have seen persistently mild temperatures and rain.

The current high over California was pinned there by such a buckle, said Jennifer Francis, a senior scientist at Woodwell Climate Research Centre in Massachusetts.

“We can’t say this particular buckling is caused by a weakened jet stream, but yes, we do expect the westerly jet-stream winds to weaken — and they already have, as greenhouse gases continue to accumulate — which tends to cause large waves like this one to occur more often,” Francis said. “Patterns like this are occurring more often and are expected to increase in the future.”

Kevin Trenberth, a distinguished scholar at the US National Centre for Atmospheric Research, said that jet-steam buckling isn’t caused  by global warming, but it can be made worse as a result of it. Deke Arndt, chief of the climate monitoring section at the National Centres for Environmental Information, said that while 2020 has been a hot year so far, with big weather events, there are more subtle changes going on that he finds more troubling.

“Summer has been a high-energy event across the US,” Arndt said. Indeed — two hurricanes and three tropical storms have hit the 48 contiguous states, including Isaias, which knocked out power to millions in New York and the northeast, and last week’s derecho, which put a few more million Americans in the dark. Then came California’s troubles.

But Arndt said faster rising overnight temperatures might be another dangerous phenomenon.

Overnight is when people, plants and animals need to cool off to recover and when you expect energy use to drop, so as the night warms, it could have far-reaching consequences. “In a lot of ways, those overnight hours are landing a harder punch on our collective health than those afternoon temperatures,” Arndt said. 

The world has warmed about 1°C since industrialisation. Much of California, other than its northern coast and areas east of Sacramento, has heated up even faster.

Across California’s Central Valley, the August heatwave brought the hottest days of the year so far to Sacramento and Fresno, which is unusual because those cities tend to reach their warmest days in July, said David Roth, a senior branch forecaster at the US Weather Prediction Centre.

In Death Valley, the high on August 16 reached 54.4°C, which, if verified,will be the hottest August reading ever and the warmest its been there since 1913, the US National Weather Service said. Globally, it would be the highest temperature recorded on Earth since 1931, the World Meteorological Organisation said.

These record-high temperatures are a sign that the entire climate system has shifted beyond what was normal during the 20th century and earlier. The new, highest-ever modern temperature reading in Death Valley is an exclamation point — the world’s most extreme location for heat is getting even hotter.

Over the weekend, California also received a dose of apocalyptic insult to add to its injury. There was just enough moisture in the atmosphere to touch off thunderstorms that — when combined with the heat rising from a wildfire north of Lake Tahoe — triggered a fire tornado.

“Climate change is catching up to us,” Moody’s Steinberg said. “There is no denying that.”

Bloomberg