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The direst possible consequences of the climate crisis for the UK have been mapped by researchers, encompassing a scorching 4C jump in average temperatures to a 6.5-foot increase in sea levels. An alternative projection foresees a plunge of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Events, Not Forecasts

These consequences, some of which are associated with irreversible climate shifts, are viewed as low probability but possible. The researchers stated that these models addressed a shortfall in forecasting that had left the UK unprepared for worst-case results.

"The climate extremes we have outlined aren’t predictions, but they are possible," said the professor who led the analysis. "The nation has been formulating policy in the absence of the methods to plan for worst-case scenarios. We've now provided planners what they need to get ready for future conditions they pray never occur, but can’t afford to ignore."

A Spectrum of Harsh Climate Projections

A further series of worst-case scenarios sets out the potential extent of harsh climate between now and the year 2100. These indicate that temperatures could soar in certain periods by up to 6C above historical levels, while precipitation could be triple normal levels.

The probability of the catastrophic events occurring cannot be precisely determined due to unknown factors about what measures will be implemented to combat global heating and how the climate system will respond. This analysis was described as similar to security threat evaluations or stress tests for the banking sector.

Major Possibility Elements

• Four-Degree Warming: Planetary heating rising well above 4C by 2100 could occur if emissions cuts breaks down or if strong feedback loops including the Amazon rainforest becoming a net carbon source emit its vast reserves of carbon. This would lead to extreme and prolonged heatwaves and droughts affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the North Atlantic current, is losing strength and becoming unstable due to global heating. A complete failure commencing by 2030 would lead to a 6C cooling in the UK. "Crop production would be severely challenged and freshwater availability would be drastically changed," explained the professor.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the Arctic and Antarctic collapse rapidly, flooding seaside communities. Unlike the other scenarios, this possibility is already recognized by planners.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if airborne particulates is sharply cut. This counterintuitive effect occurs because pollution particles from fossil fuel combustion reflect solar radiation from warming the ground.

Planning for the Extreme

The worst-case scenarios could be applied to guide the building of critical national infrastructure, including housing developments, energy plants and water management networks. Awareness of these environmental threats could also hasten the drive to slash carbon pollution.

The analysis created the extreme models using a blend of observed and historical experience, climate models and scientific theory. These outcomes exclude broader worldwide issues like the global food shortages and geopolitical instability.

The research was requested as part of a government’s adaptation planning initiative. Independent analyses have cautioned that too little consideration was being given to low‐likelihood but high‐impact risks.

The government's climate advisors has stated that the UK must "become resilient to moderate heating" and assess the threats for 4C. Previous adaptation plans have been labeled being "insufficient" by some observers.

An official statement said: "The climate emergency is at the center of this government’s agenda, both adapting for the future and establishing itself as a renewable energy leader. It is essential that the UK is resilient for the effects."