UK Climate Crisis: Scientists Reveal Worst-Case Scenarios

The worst-case impacts of the climate crisis for the United Kingdom have been outlined by scientists, including a potential 4-degree Celsius temperature rise and a 2-meter increase in sea levels, with an additional scenario projecting a 6-degree Celsius temperature drop following the collapse of key Atlantic Ocean currents, which would severely disrupt agriculture and energy systems.

The impacts, some linked to climate tipping points, are considered low-probability but plausible, the researchers said. They noted the scenarios address a gap in forecasting that had left the UK unprepared for extreme outcomes.

A separate set of worst-case scenarios details the potential extent of extreme weather through the end of the century, suggesting temperatures could spike up to 6 degrees Celsius above average in some months, while rainfall could triple normal levels.

“The climate extremes we have mapped aren’t predictions, but they are plausible,” said Nigel Arnell, a University of Reading professor who led the study. “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.”

The probability of these extreme scenarios could not be calculated due to uncertainty about future climate action and the climate system’s response. Arnell compared the analysis to national security risk assessments or the Bank of England’s financial stress tests.

“You couldn’t have known what the probability of Russia invading Ukraine was, but you could have said this is what the consequences might be,” he added.

The worst-case scenarios could inform long-term infrastructure projects such as new towns, nuclear power stations, and urban drainage systems, Arnell said, adding that awareness of climate risks could accelerate efforts to cut fossil fuel emissions.

Published in the journal Earth’s Future, the analysis developed the worst-case scenarios using a combination of observational and historical data, computer simulations, and theory.

Global temperatures rising well above 4 degrees Celsius by 2100 could occur if climate action collapses or if strong feedback loops, such as the Amazon rainforest dying and releasing its vast carbon stores, materialize. This would bring extreme and prolonged summer heatwaves and droughts to the UK, with thousands of early deaths already recorded in England during heatwaves under a 1.3-degree Celsius global temperature increase.

Temperatures could also rise by about 0.75 degrees Celsius if industrial pollution is sharply reduced, the scientists said, because aerosol particles from burning coal and heavy fuels block sunlight from reaching the ground.

A major ocean current, the Atlantic Meridional Overturning Circulation (Amoc), is weakening and losing stability due to global heating, making it one of the tipping points that most concerns scientists.

A collapse beginning in 2030 would lead to 6 degrees Celsius cooling in the UK. “Agriculture would struggle enormously and water resources would be completely altered,” said Arnell. “Our heat and energy system would be completely caught out by changing winter energy demand. It wouldn’t happen overnight, but it would be massively disruptive.”

A collapse of even one part of Amoc, the sub-polar gyre, would reduce UK temperatures by 2.5 degrees Celsius, the scientists said.

Global sea levels are already higher due to global heating, but a rise of 2.0 to 2.2 meters around the UK by 2100 could occur if glaciers in Greenland and Antarctica collapse rapidly, flooding coastal cities and towns. Unlike the other scenarios, this possibility was already known to planners.

The worst-case scenarios do not account for potential global problems, including devastation of food supplies and conflict.

The research was commissioned by the Met Office as part of the government’s climate resilience programme. A House of Lords report warned in 2021 that insufficient attention was being paid to low-likelihood but high-impact risks.

The Climate Change Committee, the government’s independent advisory body, has stated that the UK needs to “adapt to 2C and assess the risks for 4C.” Adaptation plans published in 2023 were criticized as “very weak.”

A government spokesperson said: “Climate change is at the heart of this government’s agenda, both adapting for the future and becoming a clean energy superpower. It is vital that the UK is ready for the impacts and we are helping local communities become more resilient, including by building nine new reservoirs, as well as a record £10.5bn in government funding for new flood defences to protect nearly 900,000 properties by 2036.”

The government has requested an evidence review of climate risks from the CCC, which will be published in the spring. It has also asked for guidance on climate scenarios to be used in planning.