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The gravest possible consequences of the climate crisis for the UK have been detailed by researchers, including a scorching 4C jump in average temperatures to a two-metre surge in sea levels. Another scenario envisions a decline of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would severely impact agriculture and energy demand.

Possible Outcomes, Not Guarantees

These impacts, a number of which are linked to irreversible climate shifts, are seen as unlikely but plausible. The team said that these models filled a gap in forecasting that had rendered the UK not ready for worst-case results.

"The worst-case scenarios we have outlined are not forecasts, but they are credible," said Nigel Arnell who led the research. "The nation has been formulating policy lacking the frameworks to assess extreme possibilities. We've now given planners what they need to plan for environmental results they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Projections

A further series of severe models details the possible scale of severe conditions between now and the end of the century. These suggest that temperatures could rocket in some months by up to 6C higher than average, while rainfall could be three times standard measurements.

The likelihood of the extreme scenarios coming to pass cannot be precisely determined due to uncertainty about what action will be implemented to combat global heating and how the climate system will react. This approach was likened to security threat evaluations or stress tests for economic stability.

Critical Possibility Highlights

• Four-Degree Warming: Global temperatures soaring past 4C by 2100 could occur if emissions cuts breaks down or if vicious cycles like the tropical forests perishing unleash its enormous store of carbon. This would result in intense and enduring heat domes and droughts affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the AMOC, is slowing down and showing signs of collapse due to ocean warming. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Agriculture would be severely challenged and water resources would be drastically changed," said the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in Greenland and Antarctica disintegrate quickly, flooding coastal cities and towns. Unlike the other scenarios, this risk is already understood by coastal engineers.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if industrial aerosols is sharply cut. This unexpected result occurs because tiny specks from burning coal scatter sunlight from warming the ground.

Preparing for the Extreme

The worst-case scenarios could be used to inform the building of long-term infrastructure, such as new towns, power generation facilities and flood defences. Knowledge about these climate risks could also speed the transition to slash fossil fuel emissions.

The research created the extreme models using a blend of observed and historical experience, climate models and scientific theory. These outcomes omit broader worldwide issues such as the devastation of food supplies and geopolitical instability.

The research was commissioned as part of a national adaptation planning initiative. Earlier reports have stated that too little consideration was being paid to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK must "become resilient to moderate heating" and examine the threats for 4C. Past policy documents have been criticised as being "very weak" by some observers.

An official statement said: "Global warming is at the core of this government’s agenda, both building resilience and establishing itself as a renewable energy leader. It is essential that the UK is resilient for the consequences."