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Without human-caused climate change temperatures of 40°C in the UK would have been extremely unlikely

Abstract
The 2022 heatwave is estimated to have led to at least 13 deaths from drowning. It brought challenging conditions for the NHS, with a spike in emergency calls, and care services supporting the elderly and vulnerable were put under increased stress, with a likely increase in heat-related deaths. The impacts were unequally distributed across demographics. Even within London, there are high levels of inequity in experienced temperatures, with certain, often poorer neighborhoods lacking green space, shade, and water, which can be lifelines during a heatwave. While Europe experiences heatwaves increasingly frequently over the last years, the recently observed heat in the UK has been so extreme that it is also a rare event in today’s climate. The observed temperatures averaged over 2 days were estimated to have a return period of approximately 100 years in the current climate. For the 1-day maximum temperatures over the region shown in Fig.1, the return time is estimated at 1 in 1000 years in the current climate. Note that return periods of temperatures vary between different measures and locations and are, therefore, highly uncertain. At three individual stations, the 1-day maximum temperatures are as rare as 1 in 500 years in St James Park in London, about 1 in 1000 years in Durham, and only expected on average once in 1500 years in today’s climate in Cranwell, Lincolnshire. The likelihood of observing such an event in a 1.2°C cooler world is extremely low and statistically impossible in two out of the three analyzed stations. The observational analysis shows that a UK heatwave as defined above would be about 4°C cooler in preindustrial times. To estimate how much of these observed changes is attributable to human-caused climate change, we combine climate models with the observations. It is important to highlight that all models systematically underestimate the observed trends. The combined results are thus almost certainly too conservative. Combining the results based on observational and model analysis, we find that, for both event definitions, human-caused climate change made the event at least 10 times more likely. In the models, the same event would be about 2°C less hot in a 1.2°C cooler world, which is a much smaller change in intensity than observed. This discrepancy between the modeled and observed trends and variability also hinders confidence in projections of the future trends. Heatwaves during the height of summer pose a substantial risk to human health and are potentially lethal. This risk is aggravated by climate change but also by other factors such as an aging population, urbanization, changing social structures, and levels of preparedness. The full impact is only known after a few weeks when the mortality figures have been analyzed. Effective heat emergency plans, together with accurate weather forecasts such as those issued before this heatwave, reduce impacts and are becoming even more important in light of the rising risks.
Type
Report
Type of thesis
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Citation
Date
2022-07-28
Publisher
World Weather Attribution
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© 2022 The Authors.