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The direst potential impacts of the climate crisis for the UK have been mapped by researchers, ranging from a blistering 4C increase in average temperatures to a 2-metre rise in sea level. A separate possibility foresees a plunge of 6C in temperatures following the failure of key Atlantic Ocean currents, which would profoundly upset agriculture and energy needs.

Credible Outcomes, Not Guarantees

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

"The worst-case scenarios we have detailed are not forecasts, but they are credible," commented Nigel Arnell who oversaw the analysis. "The UK has been formulating policy lacking the methods to plan for worst-case scenarios. We've now supplied decision-makers what they need to prepare for climate outcomes they hope never happen, but dare not dismiss."

A Suite of Harsh Climate Projections

Another collection of severe models maps the potential extent of severe conditions between now and the close of the 2100s. These show that thermometer readings could skyrocket in particular seasons by up to 6C higher than the norm, while precipitation could be three times normal levels.

The chance of the worst-case outcomes occurring remains uncertain due to uncertainty about what measures will be enacted to combat climate change and how the Earth's systems will react. This approach was described as similar to security threat evaluations or resilience checks for financial systems.

Critical Possibility Elements

• 4C Temperature Rise: Global temperatures exceeding 4C by 2100 could happen if climate action fails or if vicious cycles like the Amazon basin becoming a net carbon source emit its huge repository of carbon. This would cause severe and lengthy heat domes and droughts hitting the UK in summer.
• AMOC Shutdown: A key circulation system, the AMOC, is losing strength and showing signs of collapse due to ocean warming. A collapse commencing by 2030 would lead to a drastic cooling in the UK. "Crop production would be severely challenged and freshwater availability would be completely altered," said the lead researcher.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the Arctic and Antarctic melt abruptly, flooding low-lying areas. Unlike the other scenarios, this possibility is already known by coastal engineers.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if airborne particulates is drastically reduced. This paradoxical outcome occurs because aerosol particles from fossil fuel combustion scatter sunlight from reaching the ground.

Building Resilience Against the Extreme

These dire projections could be applied to guide the development of long-term infrastructure, including housing developments, energy plants and water management networks. Understanding these climate risks could also hasten the transition to slash carbon pollution.

The study formulated the worst-case scenarios using a combination of real-world events, computer simulations and climate physics. The scenarios omit international cascading effects such as the global food shortages and increased conflict.

This work was initiated as part of a government’s adaptation planning initiative. Previous assessments have cautioned that insufficient focus was being given to high-consequence, low-probability risks.

An independent advisory body has said that the UK needs to "adapt to 2C" and examine the dangers for severe warming. Previous adaptation plans have been criticised as being "inadequate" by some observers.

A national response said: "The climate emergency is at the center of the country's focus, both adapting for the future and becoming a clean energy superpower. It is crucial that the UK is prepared for the consequences."