Scientists have issued a stark warning to the UK government, revealing a series of worst-case climate crisis scenarios for which the nation must urgently prepare. The analysis, which fills a critical gap in forecasting, outlines plausible but severe outcomes including scorching temperature rises, catastrophic sea level increases, and a dramatic plunge in temperatures triggered by ocean current collapse.
Plausible Extremes: From Scorching Heat to Abrupt Cooling
The research, led by Professor Nigel Arnell from the University of Reading and published in the journal Earth's Future, maps out extreme possibilities for the end of the century. One scenario sees global temperatures soaring well above 4C by 2100, a situation that could unfold if climate action collapses or critical feedback loops are triggered, such as the die-back of the Amazon rainforest.
This 4C+ world would bring extreme and prolonged heatwaves and droughts to the UK in summer, with temperatures in some months potentially reaching up to 6C above current averages. The report grimly notes that thousands of early deaths have already occurred in England during heatwaves linked to just a 1.3C global temperature rise.
Paradoxically, scientists also warn that a rapid cut in industrial air pollution could drive temperatures up by about 0.75C, as it would reduce the sunlight-blocking effect of aerosol particles from burning coal and heavy fuels.
In a contrasting but equally disruptive scenario, the collapse of a major Atlantic Ocean current system—the Atlantic meridional overturning circulation (Amoc)—could cause UK temperatures to plunge by 6C if it began in 2030. A collapse of just one part, the sub-polar gyre, would still lead to a 2.5C cooling.
Coastal Flooding and Systemic Disruption
Another grave threat outlined is a 2.0 to 2.2 metre rise in sea levels around the UK by 2100, should glaciers in Greenland and Antarctica undergo rapid collapse. This would flood coastal cities and towns, presenting a long-term threat already familiar to planners.
Professor Arnell emphasised the profound disruption such events would cause. "Agriculture would struggle enormously and water resources would be completely altered," he stated regarding an Amoc collapse. "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."
The scientists stress that these are not predictions but plausible risk scenarios, developed using historical data, computer simulations, and theory. Their probability is uncertain due to unknowns in future climate action and the climate system's response, making the analysis akin to a national security risk assessment or a financial stress test.
A Call for Preparedness and Stronger Adaptation
The research was commissioned by the Met Office as part of the government's climate resilience programme. It addresses a warning from a 2021 House of Lords report that insufficient attention was being paid to low-likelihood, high-impact risks.
Professor Arnell argued that these scenarios are vital tools for planning long-term infrastructure like new towns, nuclear power stations, and drainage systems. "The UK has been planning without the tools to test against worst-case scenarios," he said. "We've now given decision-makers what they need to prepare for climate outcomes they hope never happen, but can't afford to ignore." He added that a clearer understanding of these severe risks could also accelerate efforts to cut fossil fuel emissions.
The government's independent Climate Change Committee (CCC) has advised that the UK needs to "adapt to 2C and assess the risks for 4C." However, the government's own adaptation plans, published in 2023, were widely criticised as being "very weak."
In response to the findings, a government spokesperson said: "Climate change is at the heart of this government's agenda... It is vital that the UK is ready for the impacts and we are helping local communities become more resilient." They cited nine new reservoirs and a record £10.5bn for new flood defences by 2036.
The government has requested an evidence review of climate risks from the CCC, due in spring, and has also asked for guidance on which climate scenarios should be used in national planning.
