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The direst projected effects of the global heating for the UK have been outlined by scientists, ranging from a searing 4C increase in mean temperatures to a 6.5-foot rise in sea level. Another scenario envisions a drop of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Plausible Events, Not Predictions

These effects, a number of which are connected to irreversible climate shifts, are seen as unlikely but credible. The scientists explained that these models addressed a shortfall in risk assessment that had left the UK ill-prepared for extreme outcomes.

"The worst-case scenarios we have detailed aren’t predictions, but they are plausible," stated the lead researcher who oversaw the analysis. "The nation has been planning in the absence of the tools to assess extreme possibilities. We've now provided policymakers what they need to plan for climate outcomes they wish to avoid, but can’t afford to ignore."

A Spectrum of Severe Conditions Scenarios

A second set of dire projections sets out the potential extent of severe conditions between now and the close of the 2100s. These show that temperatures could skyrocket in some months by up to 6C above the norm, while precipitation could be triple typical amounts.

The probability of the catastrophic events occurring remains uncertain due to a lack of certainty about what action will be taken to address global warming and how the climate system will behave. This analysis was compared to security threat evaluations or stress tests for financial systems.

Major Scenario Highlights

• 4C Temperature Rise: Planetary heating rising well above 4C by 2100 could happen if climate action breaks down or if strong feedback loops such as the Amazon basin becoming a net carbon source release its huge repository of carbon. This would result in intense and enduring heatwaves and droughts affecting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is losing strength and losing stability due to global heating. A full shutdown commencing by 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would face immense difficulties and freshwater availability would be drastically changed," said the professor.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in Greenland and Antarctica collapse rapidly, inundating low-lying areas. Unlike the other scenarios, this risk is already known by coastal engineers.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because aerosol particles from fossil fuel combustion scatter sunlight from reaching the ground.

Planning for the Worst

These dire projections could be used to inform the building of major projects, such as housing developments, power generation facilities and water management networks. Understanding these climate risks could also accelerate the transition to cut fossil fuel emissions.

The research formulated the severe projections using a blend of past data and records, computer simulations and climate physics. These outcomes do not take into account broader worldwide issues including the agricultural collapse and increased conflict.

The research was commissioned as part of a official climate resilience programme. Previous assessments have cautioned that too little consideration was being paid to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "become resilient to moderate heating" and assess the dangers for four degrees. Previous adaptation plans have been described as being "insufficient" by certain experts.

A national response noted: "The climate emergency is at the center of the country's focus, both building resilience and becoming a renewable energy leader. It is essential that the UK is ready for the consequences."