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The gravest possible consequences of the global heating for the UK have been mapped by experts, ranging from a searing 4C rise in mean temperatures to a 2-metre surge in ocean levels. An alternative projection envisions a drop of 6C in temperature following the failure of crucial Atlantic Ocean currents, which would massively disrupt farming and energy needs.

Credible Extremes, Not Forecasts

These effects, a number of which are linked to irreversible climate shifts, are seen as improbable but plausible. The team said that these projections filled a gap in risk assessment that had rendered the UK not ready for catastrophic possibilities.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are possible," commented the lead researcher who directed the study. "Britain has been making preparations lacking the tools to assess extreme possibilities. We've now provided policymakers what they need to plan for climate outcomes they wish to avoid, but must not overlook."

A Spectrum of Extreme Weather Possibilities

A second set of severe models maps the projected severity of severe conditions between now and the year 2100. These show that thermometer readings could soar in some months by up to 6C higher than the norm, while precipitation could be three times normal levels.

The probability of the worst-case outcomes happening cannot be precisely determined due to a lack of certainty about what steps will be implemented to address climate change and how the Earth's systems will react. This approach was likened to security threat evaluations or resilience checks for financial systems.

Major Possibility Details

• Four-Degree Warming: Worldwide averages rising well above 4C by 2100 could happen if climate action fails or if strong feedback loops such as the Amazon basin dying emit its enormous store of carbon. This would lead to intense and enduring heat domes and dry spells affecting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the North Atlantic current, is losing strength and losing stability due to ocean warming. A collapse commencing by 2030 would lead to a 6C cooling in the UK. "Agriculture would be severely challenged and water resources would be fundamentally reshaped," explained the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the Arctic and Antarctic disintegrate quickly, flooding seaside communities. Differing from the other scenarios, this risk is already known by planners.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if industrial aerosols is drastically reduced. This counterintuitive effect occurs because aerosol particles from burning coal reflect sunlight from warming the ground.

Planning for the Unthinkable

The severe models could be utilized in planning the construction of major projects, for example housing developments, power generation facilities and flood defences. Knowledge about these future hazards could also accelerate the drive to cut carbon pollution.

The study created the worst-case scenarios using a combination of observed and historical experience, computer simulations and climate physics. The possibilities exclude potential global problems including the devastation of food supplies and resource wars.

The research was initiated as part of a national risk assessment framework. Independent analyses have warned that insufficient focus was being allocated to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK must "become resilient to moderate heating" and assess the threats for severe warming. Earlier government strategies have been described as being "inadequate" by some observers.

A government spokesperson commented: "Global warming is at the core of the country's focus, both adapting for the future and transitioning to a renewable energy leader. It is crucial that the UK is ready for the effects."