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The gravest potential impacts of the global heating for the UK have been mapped by researchers, ranging from a searing 4C rise in average temperatures to a 2-metre surge in sea levels. An alternative projection envisions a decline of 6C in temperature following the collapse of critical Atlantic Ocean currents, which would severely impact farming and power requirements.

Plausible Events, Not Guarantees

These effects, a number of which are associated with climate tipping points, are viewed as unlikely but plausible. The researchers said that these projections filled a gap in forecasting that had left the UK not ready for catastrophic possibilities.

"The climate extremes we have detailed should not be seen as certainties, but they are credible," commented the professor who led the study. "The UK has been formulating policy lacking the tools to test against extreme possibilities. We've now provided decision-makers what they need to plan for climate outcomes they wish to avoid, but dare not dismiss."

A Spectrum of Severe Conditions Scenarios

A second set of worst-case scenarios maps the projected severity of extreme weather between now and the close of the 2100s. These show that thermometer readings could rocket in some months by up to 6C above average, while precipitation could be triple typical amounts.

The probability of the extreme scenarios happening remains uncertain due to a lack of certainty about what measures will be implemented to combat climate change and how the climate system will respond. This approach was compared to security threat evaluations or resilience checks for financial systems.

Critical Outcome Highlights

• Severe Heating: Worldwide averages rising well above 4C by 2100 could occur if climate action fails or if powerful amplifying effects like the tropical forests perishing emit its huge repository of carbon. This would cause intense and enduring heat domes and water shortages hitting the UK in summer.
• AMOC Shutdown: A key circulation system, the North Atlantic current, is losing strength and becoming unstable due to ocean warming. A full shutdown commencing by 2030 would lead to a 6C cooling in the UK. "Farming would be severely challenged and water supplies would be completely altered," noted the lead researcher.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the polar regions disintegrate quickly, flooding coastal cities and towns. In contrast to the other scenarios, this risk is already understood by infrastructure experts.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from burning coal scatter sunlight from warming the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be applied to guide the construction of major projects, such as new towns, nuclear power stations and water management networks. Knowledge about these climate risks could also speed the drive to slash greenhouse gas emissions.

The study developed the worst-case scenarios using a blend of past data and records, computer simulations and established principles. The possibilities omit international cascading effects like the agricultural collapse and geopolitical instability.

The project was requested as part of a government’s risk assessment framework. Earlier reports have warned that too little consideration was being allocated to catastrophic yet improbable risks.

An independent advisory body has stated that the UK needs to "become resilient to moderate heating" and examine the risks for severe warming. Previous adaptation plans have been described as being "very weak" by some observers.

An official statement commented: "Climate change is at the core of this government’s agenda, both building resilience and establishing itself as a clean energy superpower. It is crucial that the UK is ready for the consequences."