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The most severe possible consequences of the climate emergency for the UK have been mapped by scientists, encompassing a scorching 4C rise in average temperatures to a two-metre surge in sea levels. Another scenario foresees a drop of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would severely impact farming and power requirements.

Plausible Events, Not Predictions

These impacts, a number of which are connected to critical climate thresholds, are seen as low probability but credible. The team explained that these scenarios addressed a shortfall in forecasting that had left the UK not ready for catastrophic possibilities.

"The climate extremes we have outlined should not be seen as certainties, but they are possible," stated Nigel Arnell who led the analysis. "The nation has been making preparations without the tools to test against worst-case scenarios. We've now given policymakers what they need to plan for environmental results they hope never happen, but must not overlook."

A Suite of Extreme Weather Possibilities

A second set of worst-case scenarios details the potential extent of severe conditions between now and the close of the 2100s. These suggest that thermometer readings could rocket in particular seasons by up to 6C above average, while precipitation could be triple normal levels.

The probability of the extreme scenarios happening remains uncertain due to unknown factors about what measures will be enacted to combat global warming and how the climate system will respond. This research was likened to national security risk assessments or scenario planning for economic stability.

Critical Outcome Details

• Four-Degree Warming: Worldwide averages exceeding 4C by 2100 could happen if climate action fails or if powerful amplifying effects such as the Amazon basin dying unleash its huge repository of carbon. This would result in extreme and prolonged heatwaves and dry spells plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is losing strength and losing stability due to global heating. A complete failure starting around 2030 would lead to a 6C cooling in the UK. "Crop production would be severely challenged and water supplies would be fundamentally reshaped," noted the professor.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the polar regions collapse rapidly, submerging seaside communities. Differing from the other scenarios, this threat is already known by coastal engineers.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if airborne particulates is drastically reduced. This paradoxical outcome occurs because aerosol particles from burning coal scatter sunlight from reaching the ground.

Building Resilience Against the Unthinkable

The severe models could be used to inform the construction of long-term infrastructure, such as new towns, nuclear power stations and urban drainage systems. Understanding these climate risks could also speed the transition to cut fossil fuel emissions.

The study formulated the extreme models using a mix of real-world events, computer simulations and established principles. The scenarios omit international cascading effects including the devastation of food supplies and increased conflict.

The research was initiated as part of a government’s climate resilience programme. Earlier reports have stated that insufficient focus was being allocated to catastrophic yet improbable risks.

An independent advisory body has stated that the UK must "become resilient to moderate heating" and assess the dangers for 4C. Past policy documents have been described as being "inadequate" by environmental groups.

An official statement commented: "The climate emergency is at the center of the country's focus, both building resilience and becoming a low-carbon economy. It is vital that the UK is prepared for the consequences."