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The direst potential impacts of the climate emergency for the UK have been mapped by researchers, encompassing a scorching 4C jump in temperatures to a 6.5-foot rise in ocean levels. A separate possibility predicts a plunge of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset food production and power requirements.

Credible Extremes, Not Guarantees

These impacts, a number of which are linked to climate tipping points, are seen as improbable but plausible. The researchers said that these projections plugged a hole in planning that had left the UK ill-prepared for catastrophic possibilities.

"The climate extremes we have outlined should not be seen as certainties, but they are possible," said the professor who oversaw the study. "Britain has been making preparations lacking the frameworks to test against catastrophic outcomes. We've now supplied policymakers what they need to get ready for climate outcomes they hope never happen, but dare not dismiss."

A Spectrum of Extreme Weather Scenarios

A second set of worst-case scenarios sets out the projected severity of extreme weather between now and the close of the 2100s. These suggest that temperatures could skyrocket in some months by up to 6C higher than historical levels, while rainfall could be triple normal levels.

The probability of the extreme scenarios occurring cannot be precisely determined due to unknown factors about what action will be implemented to tackle climate change and how the climate system will react. This analysis was described as similar to security threat evaluations or stress tests for economic stability.

Key Possibility Highlights

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could happen if international cooperation fails or if strong feedback loops like the tropical forests perishing release its enormous store of carbon. This would result in extreme and prolonged heatwaves and droughts hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and becoming unstable due to ocean warming. A full shutdown beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and water resources would be fundamentally reshaped," noted the professor.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the Arctic and Antarctic melt abruptly, flooding low-lying areas. In contrast to the other scenarios, this threat is already understood by infrastructure experts.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if industrial aerosols is drastically reduced. This counterintuitive effect occurs because aerosol particles from fossil fuel combustion reflect solar radiation from warming the ground.

Building Resilience Against the Worst

The severe models could be used to inform the development of long-term infrastructure, such as expanded cities, nuclear power stations and urban drainage systems. Understanding these climate risks could also accelerate the push to reduce fossil fuel emissions.

The research created the worst-case scenarios using a combination of observed and historical experience, digital projections and established principles. The scenarios omit international cascading effects including the devastation of food supplies and geopolitical instability.

The project was requested as part of a government’s risk assessment framework. Independent analyses have warned that insufficient focus was being given to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK must "prepare for two degrees of warming" and examine the risks for four degrees. Previous adaptation plans have been criticised as being "inadequate" by some observers.

A national response commented: "Global warming is at the heart of the country's focus, both building resilience and transitioning to a clean energy superpower. It is vital that the UK is ready for the consequences."