Global warming will bring more variable temperatures in summer and less variable in winter, finds new study.

Summers in Europe will feature more unusually cooler days as well as hotter ones in the future due to climate change, new research has revealed.

While more extreme temperatures, and higher average temperatures, have long been predicted by scientists, a team of researchers have now carried out the most sophisticated study yet to fill in the gaps about how global warming will actually influence summer and winter temperatures in the northern hemisphere.

We need to make all of our systems – from agriculture, through to infrastructure, as well as softer networks, like social networks and connections – resilient to these changes. Alyssa Gilbert Director of Policy at the Grantham Institute

They found that the likelihood of temperatures rising above or falling below the new average will not be affected in the same way for different seasons and regions, and this has implications for the strategies being designed to build resilience to the changing climate.

The study, published in the journal Nature Geoscience, finds that, in addition to the predicted increase in average temperature, fluctuations in temperature around the average will become more erratic during summer in Europe.

In winter, temperature deviations relative to the new average will be less pronounced over most of the northern hemisphere, as unusually warm days become relatively less common, and unusually cold days even rarer.

Professor Sir Brian Hoskins, Chair of the Grantham Institute – Climate Change and the Environment, at Imperial College London, was co-author of the study along with colleagues at the University of Reading.

Dr Talia Tamarin-Brodsky, researcher in meteorology at the University of Reading, said: "Previous studies have assumed that hot and cold variations around the warmer future average temperature will be affected equally. However, our research shows this is not the case.

"In Europe, there will be more days in summer that are noticeably hotter or colder than the new average as temperatures vary more. In winter, colder than average days will become less likely over most of the northern hemisphere, which means that when they do come they will be even further from what we are used to, making it more difficult for human infrastructure, and the natural world, to cope."

Extremely hot days are expected to become even more stark as the average global temperature rises under climate change, but the new study was the first to explore why hot and cold fluctuations will be affected differently in the northern hemisphere, both in summer and winter.

The study was co-authored by fellow meteorologists Professor Ted Shepherd and Dr Kevin Hodges. They found that regional warming patterns in Europe expected under climate change would also affect neighbouring regions as hot and cold air masses are carried by atmospheric weather systems. This will cause different temperature deviations in different parts of the world.

Professor Hoskins said: "We all know that the climate can be expected to warm. However, relative to this warmer average climate, will cold days and warm days become more, or less, extreme? The answer to this question is very important for designing resilience to the changing climate. We find that it is not simple - it depends on whether it is winter or summer and where you are."

Alyssa Gilbert, Director of Policy and Translation at the Grantham Institute, said: "Our knowledge of the ways in which our climate will change is improving all the time.

"It is the responsibility of governments around the world to take note and prepare properly for these expected changes. We need to make all of our systems – from agriculture, through to infrastructure, as well as softer networks, like social networks and connections – resilient to these changes."

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Full reference: Tamarin, T., Hodges, K., Hoskins, B., Shepherd, T. (2020); 'Changes in northern hemisphere temperature variablity shaped by regional warming patterns'; Nature Geoscience; doi: 10.1038/s41561-020-0576-3

Header image: Caeau Pontcanna Fields, Cardiff (Jeremy Segrott / Flickr CC by 2.0)

Original reporting by Pete Bryant, University of Reading.