Extreme weather takes climate change models 'off the scale'

Scientists shocked by dramatic change in frequency of extreme events

A firefighter from New Mexico checking for smouldering debris from the Bootleg Fire near Paisley, Oregon, in the United States on Friday. A fire over an area 25 times the size of Manhattan has raged for weeks in the state, aided by a record-shatterin
A firefighter from New Mexico checking for smouldering debris from the Bootleg Fire near Paisley, Oregon, in the United States on Friday. A fire over an area 25 times the size of Manhattan has raged for weeks in the state, aided by a record-shattering heatwave. PHOTO: NYTIMES
A firefighter from New Mexico checking for smouldering debris from the Bootleg Fire near Paisley, Oregon, in the United States on Friday. A fire over an area 25 times the size of Manhattan has raged for weeks in the state, aided by a record-shatterin
Water lines visible on the steep banks of Lake Oroville on Thursday in Oroville, California. State water officials say Lake Oroville's Edward Hyatt Power Plant might be forced to shut down the hydroelectric plant as early as next month or September if water levels continue to drop. PHOTO: AGENCE FRANCE-PRESSE
A firefighter from New Mexico checking for smouldering debris from the Bootleg Fire near Paisley, Oregon, in the United States on Friday. A fire over an area 25 times the size of Manhattan has raged for weeks in the state, aided by a record-shatterin
Londoners cooling down by the fountains of Trafalgar Square on Wednesday. The Met Office has issued its first extreme heat warning for Britain as temperatures are expected to reach 33 deg C in some areas. PHOTO: EPA-EFE

LONDON • Fires, floods, heatwaves and droughts. The deadly weather that has unfolded in recent weeks has left climate scientists "shocked" and concerned that extreme events are arriving even faster than models predicted.

In southern Oregon, a fire over an area 25 times the size of Manhattan has raged for weeks, aided by a record-shattering heatwave.

In China, floods left 58 dead after a year's worth of rain fell in just a few days in the central city of Zhengzhou, causing over US$10 billion (S$13.6 billion) in damage.

And in Russia, a state of emergency has been declared in Yakutia in the Far East, where the authorities are creating artificial rain by seeding clouds with silver iodine in an attempt to put out more than 200 fires.

Climate scientists say the severity of these events is simply "off the scale" compared with what atmospheric models forecast - even when global warming is fully taken into account.

"I think I would be speaking for many climate scientists to say that we are a bit shocked at what we are seeing," says professor of climate science Chris Rapley at University College London. "There is a dramatic change in the frequency with which extreme events occur."

From the deadly flooding in Germany last week, to scorching heat in Canada, to a deluge in the Black Sea region, the pace and scale of catastrophic damage have been almost unimaginable, even for experts who have spent their lives studying it.

One driver behind many of these events is the shifting pattern of the jet stream, a fast-flowing band of air that governs weather in the Northern Hemisphere. It is becoming slower and wavier, particularly in summer months.

When the jet stream becomes slow and wobbly, high-pressure systems and low-pressure systems grow in magnitude and get stuck in place, explains Dr Michael Mann, director of the Earth System Science Centre at Pennsylvania State University.

This means heatwaves and droughts (linked to high-pressure systems) and flooding (linked to low-pressure systems) both become more persistent.

The phenomenon, known as "planetary wave resonance", is behind the recent heatwave in North America, for example, where temperatures in Western Canada hit a scorching 49 deg C.

It also contributed to the extreme heat in the Russian Arctic region, where extensive wildfires are producing toxic smoke that has blanketed the city of Yakutsk, a port city in Siberia, more well known as one of the coldest winter cities on the planet. The fires have caused one of the world's worst air pollution events, generating dangerous levels of particulate matter.

Dr Mann is worried that current models do not reproduce the jet stream behaviour accurately. "This means they are underestimating the magnitude of the impact of climate change on extreme weather events," he says.

"While the overall warming of the planet is pretty much in line with climate model predictions from decades ago, the rise in extreme weather events is exceeding the predictions," Dr Mann notes.

The world has warmed about 1.2 deg C on average since pre-industrial times, but that warming is unevenly distributed, with the Arctic region warming about three times faster than the rest of the world, largely because of the loss of reflective snow and ice.

This Arctic heating has a big impact on the jet stream, which is governed in part by the temperature difference between cool polar air and warm tropical air.

In Germany and Belgium, the slower jet stream is one factor that contributed to the flooding this month that led to the deaths of more than 120 people and destroyed towns and villages.

"We had a low-pressure field over central Europe which did not move, it was persistent and long lasting. Normally, our weather patterns moved from west to east," said researcher Fred Hattermann at the Potsdam Institute for Climate Impact Research.

"The engine for our west wind is the temperature gradient from the equator to the Arctic," he explains. Warming in the Arctic means that "this engine that we have is weakened".

Not all extreme weather events are solely related to the jet stream.

Global warming also has a direct impact on precipitation and rainfall, because warmer air can hold more moisture - about 7 per cent more water for each 1 deg C of warming. This is part of the reason why the recent floods in India and in China were so devastating, involving monsoonal cycles rather than jet stream behaviour.

In the torrential rain that drenched central China's Henan province last week, its capital Zhengzhou saw 20cm of water fall in a single hour.

The widespread flooding that swamped its subways drowned 12 passengers.

By Friday, the floods had caused dozens of deaths and 65.5 billion yuan (S$13.6 billion) worth of direct damage in Zhengzhou alone.

Unusually large volumes of water vapour were pushed inland by typhoons on China's southern coasts and became rain after being blown over mountain ranges in Henan, according to the China Meteorological Administration.

Consistent high pressure over the Sea of Japan, also known as East Sea, and north-west China meant that the rain clouds stagnated in a vortex of low pressure over Henan, becoming a slow-moving series of intense and successive storms known as the "train effect", the administration told Chinese state media.

The Chinese authorities said the volumes had exceeded anything on record for the past 5,000 years, extending to the official start date of Chinese civilisation.

Meanwhile, in north-eastern Russia, firefighting teams continue to battle more than 200 blazes. The Yakutia region has regularly experienced lows of minus 50 deg C in some places, but has recently set several records for the highest temperatures inside the Arctic Circle.

Governor Aysen Nikolayev has long been raising the alarm over the impact of global warming in his region.

"Undoubtedly, there is only one reason - global climate change," he told local television. "It is happening, we see Yakutia get hotter every year."

FINANCIAL TIMES

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A version of this article appeared in the print edition of The Sunday Times on July 25, 2021, with the headline Extreme weather takes climate change models 'off the scale'. Subscribe