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The most severe possible consequences of the climate emergency for the UK have been mapped by experts, ranging from a searing 4C jump in temperatures to a two-metre rise in ocean levels. Another scenario predicts a decline of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would severely impact farming and energy demand.

Credible Events, Not Guarantees

These impacts, some of which are connected to irreversible climate shifts, are considered as improbable but possible. The team said that these projections filled a gap in risk assessment that had left the UK ill-prepared for extreme outcomes.

"The climate extremes we have outlined should not be seen as certainties, but they are credible," commented Nigel Arnell who led the study. "The nation has been making preparations without the methods to plan for worst-case scenarios. We've now provided policymakers what they need to plan for climate outcomes they pray never occur, but can’t afford to ignore."

A Range of Harsh Climate Projections

A further series of severe models details the projected severity of extreme weather between now and the year 2100. These indicate that temperatures could soar in particular seasons by up to 6C above the norm, while rainfall could be three times standard measurements.

The probability of the worst-case outcomes occurring remains uncertain due to uncertainty about what measures will be implemented to combat climate change and how the planet's climate will respond. This analysis was likened to defence planning or resilience checks for economic stability.

Major Outcome Details

• Four-Degree Warming: Planetary heating soaring past 4C by 2100 could occur if emissions cuts fails or if strong feedback loops like the tropical forests becoming a net carbon source emit its huge repository of carbon. This would cause intense and enduring heat domes and dry spells plaguing the UK in summer.
• Ocean Circulation Failure: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is slowing down and losing stability due to climate change. A collapse starting around 2030 would lead to a drastic cooling in the UK. "Farming would be severely challenged and water supplies would be drastically changed," noted Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in Greenland and Antarctica disintegrate quickly, inundating low-lying areas. In contrast to the other scenarios, this threat is already understood by planners.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if pollution from industry is sharply cut. This paradoxical outcome occurs because pollution particles from burning coal reflect sunlight from warming the ground.

Building Resilience Against the Worst

The worst-case scenarios could be used to inform the development of critical national infrastructure, such as new towns, power generation facilities and urban drainage systems. Knowledge about these climate risks could also accelerate the drive to slash carbon pollution.

The study created the extreme models using a combination of past data and records, computer simulations and scientific theory. These outcomes do not take into account international cascading effects like the devastation of food supplies and increased conflict.

The research was commissioned as part of a government’s adaptation planning initiative. Earlier reports have cautioned that too little consideration was being allocated to low‐likelihood but high‐impact risks.

Official experts has said that the UK must "become resilient to moderate heating" and evaluate the risks for four degrees. Previous adaptation plans have been labeled being "insufficient" by certain experts.

A government spokesperson said: "Global warming is at the heart of this government’s agenda, both adapting for the future and becoming a clean energy superpower. It is crucial that the UK is prepared for the effects."