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The direst potential impacts of the climate crisis for the UK have been outlined by scientists, including a searing 4C rise in mean temperatures to a two-metre increase in sea levels. Another scenario predicts a decline of 6C in temperature following the collapse of key Atlantic Ocean currents, which would severely impact farming and energy needs.

Credible Outcomes, Not Predictions

These consequences, a number of which are associated with critical climate thresholds, are viewed as improbable but plausible. The researchers stated that these projections addressed a shortfall in risk assessment that had left the UK not ready for extreme outcomes.

"The climate extremes we have mapped are not forecasts, but they are possible," stated the lead researcher who directed the study. "The UK has been planning lacking the frameworks to plan for extreme possibilities. We've now supplied planners what they need to get ready for climate outcomes they pray never occur, but can’t afford to ignore."

A Spectrum of Extreme Weather Possibilities

A further series of dire projections details the projected severity of severe conditions between now and the year 2100. These indicate that thermometer readings could soar in certain periods by up to 6C higher than average, while precipitation could be three times normal levels.

The chance of the worst-case outcomes occurring cannot be precisely determined due to a lack of certainty about what steps will be implemented to combat global heating and how the planet's climate will respond. This approach was described as similar to security threat evaluations or resilience checks for economic stability.

Critical Scenario Elements

• Four-Degree Warming: Worldwide averages rising well above 4C by 2100 could transpire if climate action fails or if vicious cycles like the tropical forests dying emit its enormous store of carbon. This would lead to extreme and prolonged heatwaves and droughts plaguing the UK in summer.
• AMOC Shutdown: A major ocean current, the North Atlantic current, is losing strength and showing signs of collapse due to climate change. A collapse starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and water resources would be drastically changed," explained the lead researcher.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the Arctic and Antarctic collapse rapidly, submerging seaside communities. Unlike the other scenarios, this risk is already recognized by planners.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if pollution from industry is sharply cut. This counterintuitive effect occurs because aerosol particles from industrial activity block sunlight from reaching the ground.

Building Resilience Against the Worst

These dire projections could be utilized in planning the construction of long-term infrastructure, including expanded cities, nuclear power stations and flood defences. Understanding these future hazards could also accelerate the transition to reduce carbon pollution.

The research created the extreme models using a combination of past data and records, computer simulations and climate physics. The scenarios omit international cascading effects like the global food shortages and geopolitical instability.

The research was initiated as part of a national risk assessment framework. Independent analyses have warned that not enough attention was being given to catastrophic yet improbable risks.

An independent advisory body has stated that the UK needs to "prepare for two degrees of warming" and evaluate the threats for four degrees. Previous adaptation plans have been criticised as being "very weak" by environmental groups.

A national response said: "Climate change is at the core of this government’s agenda, both building resilience and becoming a low-carbon economy. It is vital that the UK is prepared for the consequences."