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The most severe projected effects of the global heating for the UK have been outlined by researchers, encompassing a searing 4C increase in temperatures to a 2-metre rise in sea levels. An alternative projection predicts a decline of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset farming and power requirements.

Possible Events, Not Predictions

These effects, a number of which are connected to irreversible climate shifts, are viewed as low probability but credible. The scientists stated that these scenarios filled a gap in planning 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 oversaw the research. "Britain has been making preparations lacking the tools to assess extreme possibilities. We've now supplied policymakers what they need to prepare for climate outcomes they wish to avoid, but must not overlook."

A Range of Extreme Weather Possibilities

A further series of severe models details the potential extent of extreme weather between now and the end of the century. These suggest that temperatures could skyrocket in some months by up to 6C higher than historical levels, while rainfall could be 300% of typical amounts.

The chance of the catastrophic events coming to pass could not be calculated due to uncertainty about what action will be taken to address global heating and how the planet's climate will react. This approach was described as similar to national security risk assessments or stress tests for economic stability.

Critical Scenario Highlights

• Severe Heating: Global temperatures soaring past 4C by 2100 could transpire if climate action fails or if vicious cycles like the Amazon rainforest becoming a net carbon source emit its huge repository of carbon. This would result in intense and enduring heat domes and water shortages affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is losing strength and becoming unstable due to ocean warming. A full shutdown starting around 2030 would lead to a 6C cooling in the UK. "Agriculture would struggle enormously and water supplies would be fundamentally reshaped," explained Arnell.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic collapse rapidly, submerging low-lying areas. Unlike the other scenarios, this possibility is already recognized by coastal engineers.
• Clean Air Warming: Global averages could also be pushed higher by about 0.75C if pollution from industry is sharply cut. This counterintuitive effect occurs because aerosol particles from fossil fuel combustion reflect sunlight from reaching the ground.

Building Resilience Against the Worst

The severe models could be used to inform the building of major projects, including new towns, nuclear power stations and urban drainage systems. Knowledge about these future hazards could also accelerate the transition to reduce greenhouse gas emissions.

The analysis formulated the extreme models using a combination of past data and records, digital projections and climate physics. The scenarios do not take into account potential global problems such as the global food shortages and increased conflict.

The research was requested as part of a national risk assessment framework. Earlier reports have stated 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 "adapt to 2C" and examine the dangers for severe warming. Earlier government strategies have been criticised as being "insufficient" by environmental groups.

An official statement said: "Climate change is at the center of this government’s agenda, both building resilience and becoming a renewable energy leader. It is vital that the UK is resilient for the consequences."