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The direst possible consequences of the climate crisis for the UK have been detailed by researchers, ranging from a blistering 4C increase in average temperatures to a 2-metre surge in sea level. Another scenario foresees a plunge of 6C in temperature following the failure of critical Atlantic Ocean currents, which would massively disrupt farming and power requirements.

Plausible Events, Not Predictions

These effects, some of which are associated with irreversible climate shifts, are seen as unlikely but possible. The scientists explained that these projections plugged a hole in risk assessment that had rendered the UK ill-prepared for catastrophic possibilities.

"The climate extremes we have mapped are not forecasts, but they are credible," stated Nigel Arnell who led the analysis. "The nation has been formulating policy without the frameworks to plan for extreme possibilities. We've now supplied policymakers what they need to prepare for future conditions they pray never occur, but must not overlook."

A Spectrum of Severe Conditions Possibilities

Another collection of dire projections sets out the potential extent of extreme weather between now and the year 2100. These indicate that thermometer readings could skyrocket in some months by up to 6C above average, while precipitation could be triple standard measurements.

The probability of the extreme scenarios occurring could not be calculated due to uncertainty about what measures will be implemented to address global heating and how the climate system will behave. This approach was described as similar to national security risk assessments or stress tests for economic stability.

Major Scenario Highlights

• 4C Temperature Rise: Worldwide averages exceeding 4C by 2100 could transpire if international cooperation collapses or if powerful amplifying effects such as the tropical forests perishing emit its enormous store of carbon. This would result in severe and lengthy heat domes and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is slowing down and showing signs of collapse due to ocean warming. A full shutdown beginning in 2030 would lead to a 6C cooling in the UK. "Agriculture would struggle enormously and water supplies would be completely altered," said Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica collapse rapidly, submerging seaside communities. Differing from the other scenarios, this threat is already understood by coastal engineers.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if pollution from industry is sharply cut. This paradoxical outcome occurs because aerosol particles from burning coal scatter sunlight from warming the ground.

Building Resilience Against the Worst

The worst-case scenarios could be used to inform the development of long-term infrastructure, including expanded cities, nuclear power stations and flood defences. Awareness of these climate risks could also speed the push to slash carbon pollution.

The research created the severe projections using a combination of real-world events, digital projections and climate physics. These outcomes do not take into account potential global problems like the devastation of food supplies and geopolitical instability.

This work was commissioned as part of a national adaptation planning initiative. Previous assessments have warned that not enough attention was being given to high-consequence, low-probability risks.

An independent advisory body has recommended that the UK needs to "prepare for two degrees of warming" and assess the risks for four degrees. Earlier government strategies have been criticised as being "insufficient" by some observers.

A government spokesperson said: "The climate emergency is at the core of the country's focus, both preparing for impacts and establishing itself as a renewable energy leader. It is essential that the UK is prepared for the effects."