UK’s worst-case climate risks laid bare for lawmakers

British policymakers planning for climate change now have detailed worst-case scenarios at their disposal, filling a gap that left the UK unprepared for extreme outcomes.

Scientists from the University of Reading have mapped out the most serious plausible climate threats facing the UK, including year-round cooling of up to 6°C if the Atlantic's currents collapse, temperature rises well above 4°C, or rapid sea level rises of over 2 metres by 2100.  

The team's research, published today(Thursday, 18 December) in the journal Earth's Future, provides the practical tools that government guidance requires but that did not previously exist. Until now, sea level rise was the only area where extreme scenarios existed.

Professor Nigel Arnell, lead author of the study, said: "The climate extremes we have mapped aren't predictions, but they are plausible. 

“The UK has been planning without the tools to test against worst-case scenarios. We've now given decision-makers what they need to prepare for climate outcomes they hope never happen, but can't afford to ignore."

Extreme changes mapped

The research team developed two sets of scenarios describing how climate could change in ways more severe than standard projections show. The scenarios describe physically plausible changes rather than likely outcomes. One set covers long-term changes up to 2100. The other describes extreme months and seasons that could occur at any time.

The six long-term scenarios show how climate could change more severely than conventional projections, and include: 

The short-term scenarios describe extreme individual months or seasons that could occur at any time. Hot months could see temperatures 4-6°C above average, while cold months could bring temperatures 4-7°C below average. Wet months could deliver rainfall 2.5-3 times the average, while dry months could see rainfall drop to just 10% of normal levels. Windy months could experience wind speeds 60-80% higher than average. 

Arnell, N. W., Hawkins, E., Shepherd, T. G., Haigh, I. D., Harvey, B. J., Wilcox, L. J., Shaffrey, L. C., & Turner, A. G. (2025). High-Impact Low-Likelihood Climate Scenarios for Risk Assessment in the UK. Earth's Future, 13(12), e2025EF006946. https://doi.org/10.1029/2025EF006946