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The most severe potential impacts of the climate crisis for the UK have been detailed by experts, encompassing a blistering 4C rise in average temperatures to a 6.5-foot surge in ocean levels. Another scenario envisions a decline of 6C in temperature following the collapse of crucial Atlantic Ocean currents, which would profoundly upset food production and power requirements.

Credible Outcomes, Not Predictions

These effects, a number of which are associated with irreversible climate shifts, are seen as improbable but possible. The scientists said that these projections filled a gap in risk assessment that had rendered the UK unprepared for catastrophic possibilities.

"The severe weather events we have detailed aren’t predictions, but they are credible," said Nigel Arnell who directed the research. "The nation has been formulating policy in the absence of the frameworks to assess worst-case scenarios. We've now provided policymakers what they need to get ready for environmental results they pray never occur, but must not overlook."

A Suite of Harsh Climate Scenarios

A further series of worst-case scenarios sets out the potential extent of extreme weather between now and the close of the 2100s. These suggest that temperatures could skyrocket in particular seasons by up to 6C higher than the norm, while precipitation could be 300% of typical amounts.

The likelihood of the worst-case outcomes coming to pass cannot be precisely determined due to uncertainty about what action will be taken to tackle climate change and how the Earth's systems will behave. This approach was described as similar to defence planning or stress tests for financial systems.

Major Scenario Elements

• Four-Degree Warming: Planetary heating soaring past 4C by 2100 could occur if emissions cuts breaks down or if vicious cycles including the Amazon basin becoming a net carbon source emit its vast reserves of carbon. This would cause severe and lengthy heatwaves and water shortages plaguing the UK in summer.
• Atlantic Current Collapse: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and losing stability due to climate change. A collapse commencing by 2030 would lead to a drastic cooling in the UK. "Crop production would be severely challenged and water supplies would be fundamentally reshaped," noted the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica collapse rapidly, flooding coastal cities and towns. Differing from the other scenarios, this threat is already understood by coastal engineers.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if industrial aerosols is rapidly cleaned up. This unexpected result occurs because aerosol particles from industrial activity reflect sunlight from warming the ground.

Preparing for the Extreme

These dire projections could be utilized in planning the building of critical national infrastructure, for example housing developments, energy plants and water management networks. Understanding these environmental threats could also accelerate the transition to reduce fossil fuel emissions.

The research formulated the severe projections using a blend of real-world events, computer simulations and established principles. The scenarios exclude international cascading effects like the agricultural collapse and resource wars.

The research was commissioned as part of a government’s adaptation planning initiative. Earlier reports have stated that insufficient focus was being allocated to high-consequence, low-probability risks.

An independent advisory body has stated that the UK needs to "adapt to 2C" and assess the risks for severe warming. Earlier government strategies have been labeled being "insufficient" by environmental groups.

An official statement commented: "Global warming is at the center of our national priorities, both adapting for the future and transitioning to a low-carbon economy. It is vital that the UK is prepared for the consequences."