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The gravest possible consequences of the climate crisis for the UK have been detailed by experts, including a searing 4C increase in mean temperatures to a two-metre surge in sea level. A separate possibility predicts a decline of 6C in temperature following the collapse of key Atlantic Ocean currents, which would massively disrupt agriculture and energy demand.

Credible Extremes, Not Forecasts

These effects, a number of which are linked to climate tipping points, are seen as low probability but credible. The researchers explained that these models plugged a hole in risk assessment that had rendered the UK ill-prepared for extreme outcomes.

"The climate extremes we have outlined aren’t predictions, but they are possible," stated the lead researcher who oversaw the analysis. "The UK has been formulating policy lacking the tools to assess extreme possibilities. We've now provided decision-makers what they need to plan for climate outcomes they pray never occur, but can’t afford to ignore."

A Spectrum of Extreme Weather Possibilities

A further series of severe models details the possible scale of harsh climate between now and the end of the century. These show that temperatures could skyrocket in certain periods by up to 6C above average, while precipitation could be three times typical amounts.

The chance of the worst-case outcomes occurring remains uncertain due to unknown factors about what steps will be enacted to address global warming and how the planet's climate will respond. This research was likened to defence planning or scenario planning for economic stability.

Major Outcome Details

• Severe Heating: Worldwide averages rising well above 4C by 2100 could occur if international cooperation fails or if strong feedback loops including the tropical forests perishing emit its huge repository of carbon. This would lead to severe and lengthy heatwaves and water shortages plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the North Atlantic current, is weakening and losing stability due to ocean warming. A collapse commencing by 2030 would lead to a drastic cooling in the UK. "Farming would face immense difficulties and water supplies would be drastically changed," noted the professor.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in Greenland and Antarctica disintegrate quickly, submerging coastal cities and towns. Differing from the other scenarios, this threat is already understood by coastal engineers.
• Pollution Paradox: Global averages could also be increased by about 0.75C if industrial aerosols is rapidly cleaned up. This counterintuitive effect occurs because aerosol particles from industrial activity block sunlight from warming the ground.

Planning for the Unthinkable

These dire projections could be used to inform the construction of critical national infrastructure, such as housing developments, nuclear power stations and water management networks. Knowledge about these environmental threats could also speed the transition to slash carbon pollution.

The research formulated the extreme models using a mix of observed and historical experience, climate models and scientific theory. These outcomes do not take into account broader worldwide issues like the agricultural collapse and increased conflict.

The project was commissioned as part of a government’s risk assessment framework. Independent analyses have stated that insufficient focus was being paid to high-consequence, low-probability risks.

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

An official statement said: "Climate change is at the center of the country's focus, both adapting for the future and becoming a renewable energy leader. It is crucial that the UK is prepared for the consequences."