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The most severe possible consequences of the climate crisis for the UK have been outlined by researchers, ranging from a searing 4C increase in temperatures to a 6.5-foot rise in ocean levels. A separate possibility envisions a decline of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would profoundly upset food production and power requirements.

Plausible Events, Not Forecasts

These consequences, a number of which are associated with irreversible climate shifts, are seen as improbable but credible. The team stated that these scenarios addressed a shortfall in risk assessment that had left the UK unprepared for catastrophic possibilities.

"The worst-case scenarios we have outlined aren’t predictions, but they are plausible," stated Nigel Arnell who directed the study. "Britain has been formulating policy in the absence of the frameworks to assess catastrophic outcomes. We've now given policymakers what they need to prepare for environmental results they pray never occur, but must not overlook."

A Suite of Extreme Weather Scenarios

A second set of severe models details the projected severity of extreme weather between now and the year 2100. These suggest that temperatures could rocket in certain periods by up to 6C above average, while precipitation could be three times standard measurements.

The chance of the extreme scenarios occurring remains uncertain due to uncertainty about what measures will be enacted to tackle global warming and how the planet's climate will respond. This analysis was compared to defence planning or stress tests for economic stability.

Critical Possibility Highlights

• Severe Heating: Planetary heating soaring past 4C by 2100 could happen if international cooperation breaks down or if vicious cycles including the tropical forests perishing release its huge repository of carbon. This would result in extreme and prolonged heatwaves and droughts hitting the UK in summer.
• AMOC Shutdown: A major ocean current, the AMOC, is weakening and becoming unstable due to ocean warming. A complete failure starting around 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would face immense difficulties and water supplies would be drastically changed," noted the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic disintegrate quickly, inundating seaside communities. Unlike the other scenarios, this possibility is already recognized by infrastructure experts.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if airborne particulates is drastically reduced. This paradoxical outcome occurs because aerosol particles from burning coal scatter solar radiation from warming the ground.

Building Resilience Against the Worst

The severe models could be applied to guide the building of critical national infrastructure, such as housing developments, nuclear power stations and urban drainage systems. Understanding these future hazards could also hasten the push to slash greenhouse gas emissions.

The analysis created the extreme models using a blend of real-world events, climate models and scientific theory. The scenarios omit broader worldwide issues like the devastation of food supplies and geopolitical instability.

This work was initiated as part of a national climate resilience programme. Earlier reports have warned that too little consideration was being paid to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK needs to "prepare for two degrees of warming" and examine the threats for four degrees. Previous adaptation plans have been described as being "inadequate" by certain experts.

A government spokesperson commented: "Climate change is at the heart of this government’s agenda, both preparing for impacts and establishing itself as a renewable energy leader. It is crucial that the UK is resilient for the consequences."