The role of climate change in ‘exceptional’ heat

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The UK is in the grip of an “exceptional” heatwave with temperatures looking likely to smash current records – set just a few years ago.

Here are answers to some of the key questions about the role of climate change in heatwaves.

– Is climate change already affecting heatwaves?

Yes. Dr Friederike Otto, one of the scientists who have pioneered studies that spell out the role of global warming in extreme weather events, has said every heatwave today is made more likely, frequent and intense by climate change.

A World Weather Attribution study into the heatwave in central and western Europe in summer 2019 that set a new record for the UK of 38.7C in Cambridge found it would have been up to 3C cooler if the climate was not changing.

The same group of international scientists, who compare what would have happened without climate change and with the current level of warming, also found that last year’s record-shattering heatwave in the US and Canada would have been “virtually impossible” without rising global temperatures.

Global temperature: difference from 1850-1900 average (PA Graphics)
Global temperature: difference from 1850-1900 average (PA Graphics)

– How does climate change affect heatwaves?

Average global temperatures have risen by as much as 1.2C since the industrial revolution as a result of human activities that put heat-trapping greenhouse gases into the atmosphere, such as burning fossil fuels.

So when naturally occurring hot periods happen, they come on top of this warming, pushing temperatures even higher than they would have been, making heatwaves more frequent and intense.

In addition, climate change can lead to drier soil conditions in some areas which means the sun’s energy heats the ground and air, rather than being used to evaporate water, adding to the heat.

And some parts of the world, such as Africa, are heating up faster than the global average, so when we get warm air flowing from the south, that also makes the heat more extreme.

– What are the consequences of more heatwaves?

Extreme heat is deadly, and heatwaves can kill thousands of people, with around 3,000 people dying in the UK in 2021 due to hot conditions, according to Dr Vikki Thompson, climate scientist at the University of Bristol.

While extreme cold is still the biggest weather killer of people in the UK, Prof Hannah Cloke of the University of Reading warns heatwaves will begin to take over as the most dangerous natural hazard in years to come without action to curb climate change.

More heatwaves will also mean more disruption to travel, health services and work and education, and the hot conditions – especially coming after dry periods such as the one seen in parts of England this year – make wildfires more likely.

– Isn’t this just like the summer of 1976 again?

No. Nigel Arnell, professor of climate system science at the University of Reading, says it was hot in 1976, but not as “extremely hot” as it is currently.

He said the impacts of that hot summer have been forgotten, and added: “It was disruptive. And it wasn’t really as extreme in temperature as what we’re experiencing at the moment.”

Dr Otto, from Grantham Institute for Climate Change, Imperial College London, acknowledges that there have been heatwaves in the past, but says the difference in 1976 was how the rest of the world looked.

“In 1976, there was a heatwave in the UK. In 2022, there are heatwaves everywhere in the world. And so have been in 2021 and 2020 and 2019,” she said.

– What about the future?

Prof Arnell says that all evidence from climate models and projections suggests heatwaves are going to get worse and more frequent.

The extent of the extremes depends on what action we take to curb greenhouse gas emissions.

A Met Office study found that the current chance of seeing days above 40C in the UK – which could happen on Tuesday – has increased due to climate change but is still very low.

But without action to curb emissions we could be seeing those kind of temperatures every three to four years in the UK by the end of the century.

If the world takes action on emissions in line with commitments in the international Paris Agreement to limit temperature rises to 1.5C or 2C above pre-industrial levels, the risk of extreme heat would be much lower.

For the UK, that means delivering on its legal target to cut emissions to zero overall – known as net zero – by 2050.

There is also a need to adapt the country to the already inevitable increase in heatwaves, through making sure new houses and buildings are built with sufficient ventilation and shading, and retrofitting existing properties.

Cities also need more green space, and trees which can shade streets and buildings and keep them cooler.

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