Climate change may have added nearly three degrees to British heatwave, say scientists

Sarah Knapton
Scientist say man-made climate change made the recent mini-heatwave twice as likely and hotter - AFP
Scientist say man-made climate change made the recent mini-heatwave twice as likely and hotter - AFP

Climate change may have added nearly three degrees to the British heatwave, scientists have calculated as July looks set to be declared the hottest ever month worldwide since records began.

The World Weather Attribution Group (WWA) said that the mini-heatwave in Britain which saw temperatures reach 101F (38.7F) for the first time last week was made twice as likely by man-made global warming.

Researchers used long term temperature observations and climate models to look at how the weather would have unfolded with or without the human influence on the climate.

The researchers say the intensity of the heatwave was increased by between 1.5 and 3C across Europe and between 1.5 and 2.5C in Britain.

“Every European heatwave we and others have analysed was found to be made much more likely and more intense due to human-induced climate change, so it was not surprising that climate change played a role,” said Dr Friederike Otto, acting director of the Environmental Change Institute at the University of Oxford and member of WWA.

“But how much more likely the heatwave is depends very strongly on the event definition: location, season, intensity and duration. 

“This July 2019 heatwave was so extreme over continental Western Europe that the observed magnitudes would have been extremely unlikely without climate change.”

The researchers say such extreme heat, such as was seen in Cambridge is currently a once in 30 year event 

“A return period of 30 years like in Cambridge, means that every year in the current climate you have about three per cent  chance of having a heatwave like that,” Dr Geert Jan van Oldenborgh, a researcher from the Netherlands who is part of the WWA.

A provisional assessment from the European Union's Copernicus Climate Change Service (C3S) and the European Centre for Medium-Range Weather Forecasts suggests that July could be the hottest ever seen.

The assessment shows that July 2019 will have been around 2.16F 1.2C above pre-industrial levels, compared with a 1.57F (less the 1C)  increase in July 2016, the previous hottest month. 

Final, confirmed data for the month will be published on Monday.

Earlier this week The Met Office confirmed that 10 of the hottest years on record have occurred since 2002.

Prof Richard Allan, Professor of climate science at the University of Reading, said: “Months which break the global temperature record, such as July 2016 and June and July 2019, are now the expectation rather than a surprise since this is entirely consistent with the increases in atmospheric carbon dioxide caused by human activities.

“Just as one swallow does not make a summer, one record month does not tell us much on its own since the fickle nature of weather systems and the slow sloshing about of the ocean can sometimes temporarily warm or cool the planet.

“However, the clustering of recent record hot years and months, the longer-term warming trend and our understanding of the physics of the atmosphere and oceans confirms that our climate is heating up, it's our fault and the way to stop this is to reduce and begin removing emissions of greenhouse gases.”

Prof Dann Mitchell, associate professor of atmosphere science at the University of Bristol, said the current global data showed July was ‘probably the warmest on record’.

“The warming trend is clear and the scientific evidence robustly points to this being caused by human induced climate change,” said Prof Mitchell.