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The gravest possible consequences of the global heating for the UK have been detailed by experts, ranging from a searing 4C rise in temperatures to a 2-metre rise in ocean levels. An alternative projection predicts a plunge of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would profoundly upset agriculture and energy demand.

Credible Events, Not Predictions

These consequences, a number of which are connected to irreversible climate shifts, are viewed as low probability but credible. The team stated that these projections filled a gap in planning that had rendered the UK not ready for extreme outcomes.

"The climate extremes we have detailed should not be seen as certainties, but they are plausible," commented the lead researcher who oversaw the analysis. "The nation has been making preparations in the absence of the tools to test against worst-case scenarios. We've now given policymakers what they need to prepare for climate outcomes they hope never happen, but can’t afford to ignore."

A Range of Harsh Climate Scenarios

A second set of dire projections maps the projected severity of extreme weather between now and the year 2100. These suggest that thermometer readings could soar in some months by up to 6C above average, while rainfall could be 300% of standard measurements.

The likelihood of the worst-case outcomes happening could not be calculated due to uncertainty about what steps will be implemented to tackle global heating and how the climate system will behave. This analysis was likened to defence planning or scenario planning for economic stability.

Critical Scenario Elements

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could occur if international cooperation breaks down or if vicious cycles including the Amazon basin dying unleash its huge repository of carbon. This would result in extreme and prolonged heat domes and dry spells plaguing the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is slowing down and losing stability due to ocean warming. A collapse beginning in 2030 would lead to a 6C cooling in the UK. "Agriculture would struggle enormously and water resources would be completely altered," noted Arnell.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic disintegrate quickly, inundating coastal cities and towns. Unlike the other scenarios, this threat is already recognized by planners.
• Aerosol Effect: Global averages could also be driven up by about 0.75C if industrial aerosols is sharply cut. This unexpected result occurs because aerosol particles from burning coal scatter solar radiation from warming the ground.

Building Resilience Against the Unthinkable

These dire projections could be utilized in planning the construction of major projects, such as new towns, energy plants and water management networks. Understanding these environmental threats could also hasten the drive to slash fossil fuel emissions.

The research created the extreme models using a blend of observed and historical experience, climate models and climate physics. The possibilities exclude broader worldwide issues like the agricultural collapse and resource wars.

This work was commissioned as part of a official adaptation planning initiative. Independent analyses have stated that insufficient focus was being allocated to high-consequence, low-probability risks.

Official experts has said that the UK must "become resilient to moderate heating" and evaluate the dangers for severe warming. Past policy documents have been criticised as being "insufficient" by certain experts.

A government spokesperson said: "Climate change is at the center of this government’s agenda, both preparing for impacts and transitioning to a low-carbon economy. It is essential that the UK is ready for the consequences."