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The direst projected effects of the climate crisis for the UK have been detailed by scientists, ranging from a blistering 4C increase in mean temperatures to a 6.5-foot surge in sea level. Another scenario envisions a drop of 6C in temperature following the collapse of key Atlantic Ocean currents, which would severely impact agriculture and energy needs.

Credible Extremes, Not Predictions

These effects, some of which are associated with critical climate thresholds, are considered as improbable but credible. The team said that these scenarios filled a gap in risk assessment that had left the UK ill-prepared for catastrophic possibilities.

"The climate extremes we have detailed should not be seen as certainties, but they are possible," stated the lead researcher who oversaw the research. "Britain has been formulating policy lacking the tools to assess worst-case scenarios. We've now given policymakers what they need to plan for future conditions they hope never happen, but must not overlook."

A Spectrum of Extreme Weather Scenarios

A further series of severe models details the projected severity of extreme weather between now and the end of the century. These indicate that thermometer readings could soar in particular seasons by up to 6C higher than average, while precipitation could be 300% of standard measurements.

The probability of the worst-case outcomes coming to pass could not be calculated due to a lack of certainty about what action will be implemented to address global warming and how the planet's climate will respond. This analysis was described as similar to defence planning or resilience checks for financial systems.

Critical Scenario Highlights

• 4C Temperature Rise: Worldwide averages exceeding 4C by 2100 could occur if international cooperation fails or if powerful amplifying effects like the Amazon basin becoming a net carbon source emit its huge repository of carbon. This would result in severe and lengthy heat domes and dry spells hitting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the North Atlantic current, is losing strength and losing stability due to global heating. A full shutdown beginning in 2030 would lead to a 6C cooling in the UK. "Farming would struggle enormously and water supplies would be completely altered," noted the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica disintegrate quickly, submerging seaside communities. Unlike the other scenarios, this possibility is already known by coastal engineers.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if airborne particulates is sharply cut. This paradoxical outcome occurs because aerosol particles from fossil fuel combustion reflect solar radiation from warming the ground.

Preparing for the Worst

The worst-case scenarios could be used to inform the development of long-term infrastructure, including housing developments, power generation facilities and flood defences. Knowledge about these climate risks could also speed the drive to slash fossil fuel emissions.

The study formulated the extreme models using a blend of observed and historical experience, computer simulations and climate physics. These outcomes do not take into account international cascading effects such as the agricultural collapse and resource wars.

The project was commissioned as part of a official climate resilience programme. Previous assessments have warned that too little consideration was being paid to high-consequence, low-probability risks.

Official experts has recommended that the UK must "adapt to 2C" and assess the threats for four degrees. Earlier government strategies have been labeled being "very weak" by certain experts.

A government spokesperson commented: "The climate emergency is at the core of the country's focus, both building resilience and transitioning to a clean energy superpower. It is vital that the UK is resilient for the effects."