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The most severe projected effects of the climate crisis for the UK have been mapped by researchers, ranging from a blistering 4C increase in mean temperatures to a two-metre surge in ocean levels. An alternative projection predicts a plunge of 6C in temperatures following the collapse of critical Atlantic Ocean currents, which would massively disrupt farming and energy needs.

Plausible Extremes, Not Guarantees

These impacts, a number of which are connected to irreversible climate shifts, are seen as improbable but possible. The scientists stated that these scenarios plugged a hole in forecasting that had left the UK unprepared for worst-case results.

"The worst-case scenarios we have mapped are not forecasts, but they are possible," stated the professor who oversaw the study. "The UK has been making preparations without the frameworks to assess catastrophic outcomes. We've now provided planners what they need to get ready for environmental results they pray never occur, but dare not dismiss."

A Spectrum of Severe Conditions Projections

A second set of dire projections details the projected severity of severe conditions between now and the close of the 2100s. These show that temperatures could rocket in particular seasons by up to 6C higher than historical levels, while rainfall could be triple normal levels.

The probability of the extreme scenarios coming to pass remains uncertain due to unknown factors about what steps will be taken to combat global warming and how the Earth's systems will behave. This approach was described as similar to national security risk assessments or scenario planning for financial systems.

Major Outcome Highlights

• Severe Heating: Worldwide averages rising well above 4C by 2100 could occur if emissions cuts fails or if strong feedback loops including the Amazon rainforest becoming a net carbon source unleash its huge repository of carbon. This would cause severe and lengthy heatwaves and droughts affecting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the North Atlantic current, is weakening and becoming unstable due to ocean warming. A complete failure starting around 2030 would lead to a 6C cooling in the UK. "Agriculture would face immense difficulties and water supplies would be completely altered," noted the professor.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic melt abruptly, inundating seaside communities. Differing from the other scenarios, this possibility is already known by infrastructure experts.
• Pollution Paradox: Global averages could also be increased by about 0.75C if industrial aerosols is sharply cut. This counterintuitive effect occurs because aerosol particles from burning coal block solar radiation from reaching the ground.

Preparing for the Unthinkable

The severe models could be used to inform the building of critical national infrastructure, for example expanded cities, nuclear power stations and urban drainage systems. Understanding these climate risks could also hasten the drive to cut fossil fuel emissions.

The research created the extreme models using a blend of observed and historical experience, computer simulations and climate physics. The scenarios do not take into account broader worldwide issues such as the devastation of food supplies and geopolitical instability.

The research was requested as part of a official climate resilience programme. Previous assessments have stated that too little consideration was being paid to high-consequence, low-probability risks.

An independent advisory body has said that the UK needs to "prepare for two degrees of warming" and evaluate the dangers for severe warming. Earlier government strategies have been criticised as being "inadequate" by some observers.

An official statement commented: "The climate emergency is at the heart of our national priorities, both preparing for impacts and establishing itself as a renewable energy leader. It is vital that the UK is resilient for the impacts."