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The most severe possible consequences of the climate emergency for the UK have been mapped by researchers, encompassing a scorching 4C jump in temperatures to a 6.5-foot surge in ocean levels. A separate possibility foresees a decline of 6C in temperature following the collapse of critical Atlantic Ocean currents, which would profoundly upset food production and energy demand.

Possible Extremes, Not Predictions

These effects, some of which are associated with critical climate thresholds, are viewed as improbable but plausible. The scientists explained that these projections plugged a hole in planning that had rendered the UK not ready for catastrophic possibilities.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are credible," said Nigel Arnell who led the research. "The nation has been planning in the absence of the methods to plan for catastrophic outcomes. We've now provided decision-makers what they need to plan for environmental results they hope never happen, but can’t afford to ignore."

A Spectrum of Harsh Climate Scenarios

A second set of dire projections sets out the potential extent of extreme weather between now and the end of the century. These indicate that thermometer readings could skyrocket in certain periods by up to 6C above average, while precipitation could be three times typical amounts.

The probability of the worst-case outcomes happening cannot be precisely determined due to uncertainty about what steps will be enacted to tackle climate change and how the climate system will respond. This analysis was likened to security threat evaluations or scenario planning for financial systems.

Major Possibility Details

• 4C Temperature Rise: Global temperatures rising well above 4C by 2100 could transpire if international cooperation breaks down or if powerful amplifying effects like the Amazon rainforest perishing unleash its huge repository of carbon. This would cause intense and enduring heat domes and dry spells affecting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is weakening and becoming unstable due to global heating. A complete failure beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and freshwater availability would be fundamentally reshaped," noted the lead researcher.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the Arctic and Antarctic disintegrate quickly, submerging coastal cities and towns. Unlike the other scenarios, this risk is already recognized by infrastructure experts.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if airborne particulates is rapidly cleaned up. This counterintuitive effect occurs because aerosol particles from burning coal reflect solar radiation from warming the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be used to inform the development of major projects, for example new towns, energy plants and flood defences. Knowledge about these future hazards could also hasten the push to cut carbon pollution.

The study created the extreme models using a blend of observed and historical experience, computer simulations and established principles. These outcomes do not take into account international cascading effects such as the global food shortages and increased conflict.

This work was requested as part of a national risk assessment framework. Independent analyses have cautioned that too little consideration was being paid to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK must "prepare for two degrees of warming" and assess the threats for four degrees. Earlier government strategies have been criticised as being "insufficient" by certain experts.

A government spokesperson commented: "Climate change is at the core of our national priorities, both building resilience and becoming a renewable energy leader. It is crucial that the UK is ready for the consequences."