Sudden flips from hot to cold temperature come with climate change, says study

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Rapid temperature flips from heatwaves to cold and vice versa have increased across the world and are expected to rise as a result of climate change, putting stress on human health and ecosystems, the latest research finds.

The study, published in the journal Nature Communications this week, said that between 1961 and 2023, more than 60 per cent of the world had experienced more frequent, intense and more rapid flips between extreme temperatures.

The pattern was attributed in some part to the increased “waviness” of the jet stream that encircles the planet, as well as to changes in evaporation.

“Climate warming is expected to exacerbate soil moisture deficit in some areas, which can intensify temperature variability via increasing the effects of surface heat fluxes,” the study says.

However, a scientist who was not involved in the study said the physics involved in the explanation were “challenging”.

The study identified the broad regions of west of Europe, south and south-east Asia, South America and Africa as those that experienced the greatest effects.

This increased the risk of significant and potentially irreversible impacts on human health, infrastructure, and plant phenology, leading to “cascading effects”, according to Wei Zhang, professor at Utah State University and one of the authors.

The authors said that while a growing body of research had looked at extreme warmth, such as heatwaves, or cold events, little was known about rapid flips between temperature extremes. 

But they concluded that such sudden shifts allowed “a very short time for human and ecosystem preparedness to respond and adapt”.

More frequent and intense temperature flips could also put significant strain on energy systems due to unpredictable surges in heating or cooling demand.

The study identified notable examples, such as a warm-to-cold flip in March 2012 in North America where the temperature dropped from about 10C above normal to 5C below normal in less than a week. The warmth had led to a “false spring” with premature blossoming of plants and crops that were then damaged by the abrupt cold spell. 

In September 2020, the researchers said the Rocky Mountains experienced a sudden shift from severe heatwave to a heavy blanket of snow after a drop of more than 20C within a day, resulting in power cuts and property damage. 

Similarly, Europe in April 2021 experienced a rapid swing in temperatures from warm to cold, leading to widespread frost damage to crops.

The researchers, led by academics from China, looked at an abrupt change of one standard deviation above to below the mean temperature, and vice versa, within five days, at a global scale during the more than six decade study period starting in 1961.

They also modelled the likelihood of such flips in the future, finding that under a “business as usual” scenario — where society fails to cut greenhouse gas emissions — temperature flips are projected to increase in intensity and frequency, with a shortening timeframe between extremes.

The authors said the proportion of the global population exposed to such temperature flips could more than double, and low-income countries would be expected to bear the brunt.

Mat Collins, joint Met Office chair in climate change at Exeter university, said the study was credible in its analysis of “a potentially unexpected consequence of climate change”.

“The results need to be tested using different models and different measures of ‘flips’ but it could be that climate change brings more variable weather. The mechanisms put forward seem plausible to me,” he said.

“Luckily, weather forecasts are much more reliable these days so we have a better chance of knowing if a cold or warm spell is coming over the next few days, so we can prepare.”

Richard Allan, professor of climate science at Reading university, said the research “is quite novel though it is challenging to interpret the physics explaining the weather events that generate the largest flips in temperature”.

He added that “wilder swings” between warm and cold, and wet and dry, “make managing energy and water resources more challenging”.

“The only way to limit the growing severity of weather extremes is to rapidly cut greenhouse gas emissions across all sectors of society.”

The research follows on the heels of a study by academics at Bristol and Cardiff universities that also found a flip between wet and dry conditions in cities around the world.

Some 15 per cent of the world’s most populous cities were experiencing “climate whiplash”, an intensification and flipping between drought and wet conditions, the study backed by charity WaterAid found.