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The direst potential impacts of the global heating for the UK have been mapped by researchers, including a searing 4C increase in temperatures to a two-metre rise in sea level. An alternative projection predicts a drop of 6C in temperatures following the failure of critical Atlantic Ocean currents, which would profoundly upset food production and energy demand.

Possible Outcomes, Not Predictions

These consequences, some of which are connected to climate tipping points, are viewed as improbable but possible. The scientists said that these models plugged a hole in risk assessment that had left the UK not ready for extreme outcomes.

"The climate extremes we have detailed are not forecasts, but they are credible," said Nigel Arnell who led the research. "The nation has been planning without the frameworks to plan for worst-case scenarios. We've now supplied planners what they need to plan for environmental results they wish to avoid, but must not overlook."

A Suite of Extreme Weather Scenarios

A second set of severe models sets out the possible scale of extreme weather between now and the end of the century. These indicate that thermometer readings could rocket in some months by up to 6C higher than historical levels, while precipitation could be triple normal levels.

The chance of the catastrophic events happening remains uncertain due to uncertainty about what action will be implemented to address global heating and how the planet's climate will respond. This research was described as similar to defence planning or resilience checks for the banking sector.

Critical Possibility Details

• Severe Heating: Planetary heating rising well above 4C by 2100 could occur if climate action collapses or if vicious cycles such as the tropical forests perishing release its huge repository of carbon. This would lead to extreme and prolonged heatwaves and droughts plaguing the UK in summer.
• Ocean Circulation Failure: A key circulation system, the North Atlantic current, is weakening and losing stability due to climate change. A complete failure commencing by 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would be severely challenged and freshwater availability would be fundamentally reshaped," noted Arnell.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in the polar regions melt abruptly, submerging coastal cities and towns. In contrast to the other scenarios, this possibility is already recognized 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 pollution particles from fossil fuel combustion reflect solar radiation from reaching the ground.

Preparing for the Unthinkable

The severe models could be applied to guide the construction of critical national infrastructure, for example housing developments, nuclear power stations and water management networks. Understanding these environmental threats could also accelerate the push to cut carbon pollution.

The research formulated the worst-case scenarios using a blend of real-world events, climate models and established principles. The scenarios omit international cascading effects like the agricultural collapse and geopolitical instability.

The project was requested as part of a national climate resilience programme. Previous assessments have cautioned that too little consideration was being allocated to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "prepare for two degrees of warming" and evaluate the threats for severe warming. Earlier government strategies have been criticised as being "insufficient" by certain experts.

A government spokesperson noted: "Climate change is at the heart of our national priorities, both adapting for the future and establishing itself as a clean energy superpower. It is crucial that the UK is ready for the impacts."