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The most severe potential impacts of the climate emergency for the UK have been mapped by experts, encompassing a scorching 4C rise in mean temperatures to a two-metre rise in sea level. An alternative projection envisions a drop of 6C in temperature following the collapse of crucial Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Plausible Extremes, Not Predictions

These impacts, some of which are associated with critical climate thresholds, are seen as low probability but plausible. The researchers said that these models filled a gap in planning that had rendered the UK not ready for worst-case results.

"The worst-case scenarios we have outlined aren’t predictions, but they are possible," said the lead researcher who oversaw the analysis. "Britain has been making preparations without the frameworks to plan for extreme possibilities. We've now provided planners what they need to prepare for environmental results they pray never occur, but must not overlook."

A Spectrum of Harsh Climate Projections

Another collection of dire projections maps the possible scale of severe conditions between now and the year 2100. These indicate that thermometer readings could rocket in certain periods by up to 6C above the norm, while precipitation could be 300% of typical amounts.

The likelihood of the worst-case outcomes coming to pass remains uncertain due to uncertainty about what steps will be implemented to tackle global warming and how the planet's climate will react. This research was described as similar to security threat evaluations or scenario planning for the banking sector.

Critical Scenario Elements

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could happen if international cooperation breaks down or if powerful amplifying effects such as the Amazon rainforest becoming a net carbon source release its huge repository of carbon. This would cause extreme and prolonged heat domes and water shortages affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is weakening and becoming unstable due to global heating. A collapse beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would face immense difficulties and water supplies would be fundamentally reshaped," explained Arnell.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the polar regions collapse rapidly, flooding low-lying areas. Differing from the other scenarios, this risk is already understood by infrastructure experts.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if industrial aerosols is rapidly cleaned up. This unexpected result occurs because aerosol particles from fossil fuel combustion scatter sunlight from reaching the ground.

Planning for the Extreme

These dire projections could be used to inform the building of long-term infrastructure, such as new towns, power generation facilities and flood defences. Knowledge about these environmental threats could also speed the push to cut fossil fuel emissions.

The research formulated the severe projections using a blend of observed and historical experience, digital projections and scientific theory. The possibilities omit potential global problems such as the global food shortages and resource wars.

The project was requested as part of a official climate resilience programme. Independent analyses have stated that insufficient focus was being given to catastrophic yet improbable risks.

An independent advisory body has said that the UK needs to "adapt to 2C" and evaluate the risks for severe warming. Previous adaptation plans have been described as being "very weak" by some observers.

An official statement said: "The climate emergency is at the core of the country's focus, both building resilience and transitioning to a clean energy superpower. It is essential that the UK is prepared for the consequences."