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The direst potential impacts of the global heating for the UK have been outlined by scientists, including a searing 4C jump in mean temperatures to a 6.5-foot rise in sea levels. A separate possibility foresees a drop of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would severely impact farming and power requirements.

Credible Extremes, Not Forecasts

These impacts, a number of which are associated with climate tipping points, are viewed as unlikely but plausible. The team stated that these projections plugged a hole in forecasting that had rendered the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are possible," commented the professor who led the research. "The nation has been making preparations without the tools to plan for extreme possibilities. We've now given planners what they need to prepare for future conditions they wish to avoid, but must not overlook."

A Spectrum of Harsh Climate Possibilities

A further series of severe models sets out the projected severity of extreme weather between now and the end of the century. These indicate that temperatures could rocket in some months by up to 6C higher than the norm, while rainfall could be three times normal levels.

The probability of the extreme scenarios happening could not be calculated due to unknown factors about what steps will be taken to combat global warming and how the planet's climate will react. This research was described as similar to security threat evaluations or resilience checks for financial systems.

Key Scenario Elements

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could occur if emissions cuts fails or if vicious cycles such as the Amazon rainforest becoming a net carbon source release its enormous store of carbon. This would result in extreme and prolonged heat domes and dry spells plaguing the UK in summer.
• Atlantic Current Collapse: A critical sea current, the AMOC, is weakening and becoming unstable due to global heating. A full shutdown starting around 2030 would lead to a drastic cooling in the UK. "Crop production would face immense difficulties and freshwater availability would be completely altered," said Arnell.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic disintegrate quickly, inundating coastal cities and towns. Differing from the other scenarios, this risk is already recognized by infrastructure experts.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if industrial aerosols is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from fossil fuel combustion scatter sunlight from reaching the ground.

Preparing for the Unthinkable

These dire projections could be used to inform the construction of major projects, for example new towns, energy plants and water management networks. Awareness of these future hazards could also hasten the transition to reduce carbon pollution.

The analysis developed the severe projections using a blend of observed and historical experience, digital projections and established principles. These outcomes omit international cascading effects including the devastation of food supplies and increased conflict.

The research was requested as part of a government’s risk assessment framework. Earlier reports have warned that not enough attention was being given to catastrophic yet improbable risks.

Official experts has stated that the UK must "become resilient to moderate heating" and assess the risks for four degrees. Previous adaptation plans have been described as being "inadequate" by certain experts.

A national response commented: "Global warming is at the core of the country's focus, both adapting for the future and establishing itself as a low-carbon economy. It is vital that the UK is prepared for the consequences."