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The gravest possible consequences of the climate crisis for the UK have been mapped by scientists, encompassing a scorching 4C rise in average temperatures to a 6.5-foot surge in sea level. An alternative projection foresees a decline of 6C in temperatures following the shutdown of critical Atlantic Ocean currents, which would severely impact agriculture and energy needs.

Plausible Events, Not Guarantees

These effects, a number of which are linked to critical climate thresholds, are viewed as improbable but plausible. The researchers said that these models addressed a shortfall in forecasting that had left the UK not ready for worst-case results.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are possible," stated the professor who directed the analysis. "The nation has been formulating policy lacking the tools to plan for extreme possibilities. We've now supplied planners what they need to plan for climate outcomes they hope never happen, but dare not dismiss."

A Spectrum of Harsh Climate Scenarios

A second set of severe models sets out the potential extent of severe conditions between now and the close of the 2100s. These indicate that thermometer readings could skyrocket in certain periods by up to 6C higher than average, while rainfall could be triple normal levels.

The chance of the worst-case outcomes occurring could not be calculated due to unknown factors about what measures will be implemented to combat climate change and how the climate system will respond. This approach was described as similar to national security risk assessments or stress tests for financial systems.

Key Outcome Elements

• Four-Degree Warming: Planetary heating soaring past 4C by 2100 could happen if emissions cuts fails or if strong feedback loops such as the tropical forests dying release its enormous store of carbon. This would lead to severe and lengthy heatwaves and dry spells affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the North Atlantic current, is weakening and showing signs of collapse due to climate change. A complete failure commencing by 2030 would lead to a six-degree temperature drop in the UK. "Farming would face immense difficulties and water resources would be completely altered," said Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the polar regions melt abruptly, flooding seaside communities. In contrast to the other scenarios, this risk is already recognized by coastal engineers.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if airborne particulates is rapidly cleaned up. This paradoxical outcome occurs because aerosol particles from fossil fuel combustion reflect solar radiation from warming the ground.

Preparing for the Extreme

The severe models could be used to inform the construction of long-term infrastructure, such as housing developments, nuclear power stations and water management networks. Awareness of these environmental threats could also hasten the transition to reduce carbon pollution.

The research developed the extreme models using a blend of past data and records, computer simulations and climate physics. The scenarios omit international cascading effects including the devastation of food supplies and resource wars.

This work was initiated as part of a government’s climate resilience programme. Independent analyses have stated that insufficient focus was being paid to high-consequence, low-probability risks.

Official experts has stated that the UK must "adapt to 2C" and examine the risks for 4C. Previous adaptation plans have been described as being "insufficient" by certain experts.

A government spokesperson commented: "The climate emergency is at the center of our national priorities, both preparing for impacts and establishing itself as a renewable energy leader. It is essential that the UK is prepared for the consequences."