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The most severe possible consequences of the climate emergency for the UK have been mapped by researchers, including a scorching 4C increase in mean temperatures to a two-metre surge in sea levels. Another scenario envisions a decline of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would massively disrupt farming and energy demand.

Possible Events, Not Forecasts

These effects, some of which are linked to irreversible climate shifts, are considered as improbable but possible. The team said that these models filled a gap in planning that had rendered the UK ill-prepared for worst-case results.

"The severe weather events we have detailed should not be seen as certainties, but they are credible," said the lead researcher who led the study. "The nation has been formulating policy in the absence of the tools to assess catastrophic outcomes. We've now provided planners what they need to plan for climate outcomes they hope never happen, but can’t afford to ignore."

A Suite of Harsh Climate Scenarios

A second set of severe models sets out the possible scale of extreme weather between now and the year 2100. These show that temperatures could skyrocket in some months by up to 6C higher than historical levels, while precipitation could be three times normal levels.

The chance of the worst-case outcomes coming to pass cannot be precisely determined due to unknown factors about what steps will be enacted to combat climate change and how the climate system will react. This analysis was described as similar to defence planning or resilience checks for financial systems.

Key Outcome Elements

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could occur if climate action collapses or if powerful amplifying effects including the Amazon rainforest becoming a net carbon source emit its enormous store of carbon. This would result in extreme and prolonged heat domes and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A critical sea current, 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 six-degree temperature drop in the UK. "Farming would struggle enormously and water supplies would be fundamentally reshaped," said the professor.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the polar regions disintegrate quickly, flooding coastal cities and towns. Differing from the other scenarios, this threat 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 industrial activity reflect sunlight from reaching the ground.

Preparing for the Unthinkable

The severe models could be used to inform the building of major projects, including housing developments, nuclear power stations and water management networks. Awareness of these climate risks could also speed the transition to reduce greenhouse gas emissions.

The research developed the extreme models using a mix of past data and records, computer simulations and climate physics. The possibilities exclude broader worldwide issues including the devastation of food supplies and geopolitical instability.

The project was requested as part of a official risk assessment framework. Previous assessments have warned that not enough attention was being given to high-consequence, low-probability risks.

Official experts has stated that the UK must "adapt to 2C" and evaluate the threats for four degrees. Earlier government strategies have been described as being "very weak" by certain experts.

A government spokesperson said: "Climate change is at the center of this government’s agenda, both adapting for the future and becoming a renewable energy leader. It is crucial that the UK is ready for the effects."