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The direst possible consequences of the climate crisis for the UK have been outlined by experts, ranging from a searing 4C increase in average temperatures to a two-metre increase in sea level. Another scenario envisions a decline of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would severely impact agriculture and energy needs.

Possible Outcomes, Not Predictions

These impacts, a number of which are associated with critical climate thresholds, are seen as low probability but possible. The scientists said that these projections addressed a shortfall in forecasting that had rendered the UK unprepared for catastrophic possibilities.

"The climate extremes we have mapped should not be seen as certainties, but they are plausible," said Nigel Arnell who oversaw the research. "The nation has been making preparations in the absence of the tools to plan for extreme possibilities. We've now provided policymakers what they need to plan for future conditions they hope never happen, but can’t afford to ignore."

A Range of Extreme Weather Projections

Another collection of severe models details the projected severity of extreme weather between now and the year 2100. These show that thermometer readings could rocket in particular seasons by up to 6C higher than the norm, while precipitation could be three times typical amounts.

The likelihood of the extreme scenarios occurring remains uncertain due to uncertainty about what steps will be enacted to address global heating and how the climate system will behave. This analysis was described as similar to national security risk assessments or stress tests for financial systems.

Critical Outcome Highlights

• Severe Heating: Worldwide averages exceeding 4C by 2100 could happen if emissions cuts breaks down or if strong feedback loops like the tropical forests perishing emit its enormous store of carbon. This would cause extreme and prolonged heat domes and droughts hitting the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is losing strength and showing signs of collapse due to climate change. A complete failure commencing by 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and water supplies would be completely altered," noted the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica disintegrate quickly, inundating low-lying areas. Unlike the other scenarios, this risk is already recognized by planners.
• Aerosol Effect: Global averages could also be driven up by about 0.75C if airborne particulates is sharply cut. This unexpected result occurs because aerosol particles from industrial activity reflect sunlight from warming the ground.

Planning for the Extreme

These dire projections could be used to inform the construction of long-term infrastructure, for example new towns, power generation facilities and flood defences. Knowledge about these environmental threats could also hasten the transition to reduce fossil fuel emissions.

The research developed the extreme models using a blend of past data and records, digital projections and climate physics. The possibilities exclude potential global problems such as the devastation of food supplies and increased conflict.

This work was commissioned as part of a national climate resilience programme. Independent analyses have stated that insufficient focus was being allocated to high-consequence, low-probability risks.

An independent advisory body has recommended that the UK needs to "become resilient to moderate heating" and assess the dangers for 4C. Previous adaptation plans have been labeled being "inadequate" by certain experts.

A government spokesperson said: "Climate change is at the center of the country's focus, both preparing for impacts and becoming a renewable energy leader. It is essential that the UK is prepared for the effects."