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The most severe possible consequences of the climate crisis for the UK have been outlined by scientists, ranging from a searing 4C jump in average temperatures to a 6.5-foot increase in sea levels. Another scenario foresees a drop of 6C in temperatures following the failure of critical Atlantic Ocean currents, which would profoundly upset food production and power requirements.

Credible Events, Not Guarantees

These effects, a number of which are linked to irreversible climate shifts, are seen as improbable but plausible. The team explained that these models addressed a shortfall in forecasting that had left the UK ill-prepared for extreme outcomes.

"The climate extremes we have outlined are not forecasts, but they are credible," commented Nigel Arnell who led the research. "The UK has been planning in the absence of the frameworks to plan for catastrophic outcomes. We've now given decision-makers what they need to get ready for climate outcomes they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Projections

A second set of severe models sets out the potential extent of severe conditions between now and the year 2100. These suggest that thermometer readings could skyrocket in particular seasons by up to 6C above historical levels, while precipitation could be three times typical amounts.

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

Major Outcome Elements

• Severe Heating: Worldwide averages rising well above 4C by 2100 could happen if climate action collapses or if vicious cycles such as the Amazon basin becoming a net carbon source release its vast reserves of carbon. This would cause extreme and prolonged heat domes and dry spells hitting the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is losing strength and losing stability due to climate change. A complete failure commencing by 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and water supplies would be completely altered," noted the lead researcher.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the Arctic and Antarctic collapse rapidly, inundating coastal cities and towns. Differing from the other scenarios, this possibility is already known by infrastructure experts.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because pollution particles from industrial activity reflect sunlight from warming the ground.

Planning for the Worst

These dire projections could be used to inform the building of critical national infrastructure, including housing developments, power generation facilities and water management networks. Awareness of these future hazards could also accelerate the push to slash greenhouse gas emissions.

The analysis formulated the extreme models using a blend of real-world events, digital projections and scientific theory. The scenarios exclude international cascading effects such as the devastation of food supplies and increased conflict.

This work was commissioned as part of a government’s climate resilience programme. Earlier reports have cautioned that not enough attention was being given to catastrophic yet improbable risks.

Official experts has recommended that the UK needs to "adapt to 2C" and evaluate the dangers for severe warming. Previous adaptation plans have been criticised as being "insufficient" by environmental groups.

A national response commented: "Climate change is at the heart of this government’s agenda, both adapting for the future and transitioning to a low-carbon economy. It is crucial that the UK is resilient for the effects."