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The gravest potential impacts of the climate crisis for the UK have been outlined by researchers, encompassing a scorching 4C increase in average temperatures to a 6.5-foot increase in sea level. Another scenario envisions a drop of 6C in temperature following the collapse of critical Atlantic Ocean currents, which would severely impact food production and energy demand.

Plausible Outcomes, Not Predictions

These consequences, a number of which are linked to critical climate thresholds, are seen as low probability but plausible. The scientists said that these projections addressed a shortfall in planning that had left the UK ill-prepared for extreme outcomes.

"The climate extremes we have detailed should not be seen as certainties, but they are possible," said Nigel Arnell who oversaw the study. "The nation has been formulating policy without the methods to test against worst-case scenarios. We've now supplied planners what they need to plan for climate outcomes they pray never occur, but can’t afford to ignore."

A Spectrum of Severe Conditions Projections

A further series of worst-case scenarios details the projected severity of severe conditions between now and the close of the 2100s. These suggest that temperatures could rocket in some months by up to 6C above the norm, while rainfall could be triple standard measurements.

The probability of the catastrophic events coming to pass could not be calculated due to uncertainty about what action will be taken to tackle global warming and how the planet's climate will respond. This approach was described as similar to defence planning or stress tests for economic stability.

Critical Scenario Elements

• 4C Temperature Rise: Planetary heating soaring past 4C by 2100 could transpire if international cooperation fails or if vicious cycles such as the Amazon rainforest perishing release its vast reserves of carbon. This would cause intense and enduring heatwaves and dry spells plaguing the UK in summer.
• Atlantic Current Collapse: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is slowing down and showing signs of collapse due to ocean warming. A collapse beginning in 2030 would lead to a drastic cooling in the UK. "Crop production would face immense difficulties and water supplies would be completely altered," said the professor.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in Greenland and Antarctica collapse rapidly, submerging coastal cities and towns. In contrast to the other scenarios, this threat is already recognized by infrastructure experts.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if pollution from industry is sharply cut. This paradoxical outcome occurs because aerosol particles from burning coal block sunlight from warming the ground.

Preparing for the Unthinkable

The severe models could be utilized in planning the construction of major projects, including new towns, power generation facilities and flood defences. Knowledge about these environmental threats could also hasten the push to cut greenhouse gas emissions.

The research created the severe projections using a combination of real-world events, computer simulations and established principles. The scenarios omit potential global problems like the global food shortages and increased conflict.

The research was initiated as part of a government’s climate resilience programme. Previous assessments have cautioned that not enough attention was being given to high-consequence, low-probability risks.

The government's climate advisors has said that the UK needs to "become resilient to moderate heating" and assess the threats for four degrees. Past policy documents have been criticised as being "very weak" by certain experts.

An official statement said: "Climate change is at the core of our national priorities, both building resilience and establishing itself as a clean energy superpower. It is vital that the UK is prepared for the consequences."