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The direst possible consequences of the climate crisis for the UK have been outlined by experts, including a searing 4C increase in average temperatures to a 6.5-foot increase in sea levels. An alternative projection predicts a drop of 6C in temperature following the collapse of key Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Possible Extremes, Not Forecasts

These consequences, certain ones are connected to critical climate thresholds, are viewed as unlikely but plausible. The researchers explained that these scenarios filled a gap 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 credible," commented the lead researcher who led the analysis. "The UK has been planning without the frameworks to plan for worst-case scenarios. We've now given policymakers what they need to prepare for future conditions they hope never happen, but can’t afford to ignore."

A Range of Extreme Weather Possibilities

Another collection of dire projections sets out the possible scale of extreme weather between now and the close of the 2100s. These show that temperatures could skyrocket in some months by up to 6C above historical levels, while precipitation could be 300% of normal levels.

The likelihood of the catastrophic events happening remains uncertain due to uncertainty about what steps will be taken to address global heating and how the climate system will react. This approach was described as similar to security threat evaluations or resilience checks for the banking sector.

Key Outcome Details

• Four-Degree Warming: Planetary heating exceeding 4C by 2100 could transpire if international cooperation breaks down or if powerful amplifying effects such as the Amazon basin becoming a net carbon source release its huge repository of carbon. This would cause extreme and prolonged heat domes and dry spells plaguing the UK in summer.
• AMOC Shutdown: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is weakening and becoming unstable due to ocean warming. A full shutdown starting around 2030 would lead to a 6C cooling in the UK. "Farming would be severely challenged and water resources would be drastically changed," noted the professor.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica melt abruptly, flooding low-lying areas. Unlike the other scenarios, this possibility is already known by planners.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if airborne particulates is sharply cut. This unexpected result occurs because aerosol particles from burning coal reflect solar radiation from reaching the ground.

Building Resilience Against the Extreme

The worst-case scenarios could be used to inform the development of major projects, including new towns, energy plants and flood defences. Knowledge about these future hazards could also speed the push to cut greenhouse gas emissions.

The study created the worst-case scenarios using a mix of observed and historical experience, computer simulations and climate physics. These outcomes do not take into account potential global problems such as the global food shortages and geopolitical instability.

The research was initiated as part of a national risk assessment framework. Earlier reports have cautioned that insufficient focus was being given to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK must "prepare for two degrees of warming" and evaluate the risks for 4C. Previous adaptation plans have been criticised as being "very weak" by environmental groups.

A government spokesperson said: "The climate emergency is at the heart of this government’s agenda, both building resilience and establishing itself as a renewable energy leader. It is essential that the UK is prepared for the consequences."