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The most severe possible consequences of the climate emergency for the UK have been mapped by researchers, ranging from a scorching 4C increase in temperatures to a 2-metre surge in sea levels. A separate possibility predicts a drop of 6C in temperature following the collapse of key Atlantic Ocean currents, which would massively disrupt food production and energy needs.

Possible Outcomes, Not Forecasts

These effects, certain ones are connected to climate tipping points, are viewed as low probability but credible. The scientists explained that these projections plugged a hole in planning that had left the UK ill-prepared for catastrophic possibilities.

"The climate extremes we have detailed are not forecasts, but they are plausible," commented Nigel Arnell who led the analysis. "The nation has been planning without the methods to test against extreme possibilities. We've now provided decision-makers what they need to plan for climate outcomes they hope never happen, but can’t afford to ignore."

A Range of Extreme Weather Projections

A further series of worst-case scenarios maps the potential extent of harsh climate between now and the year 2100. These indicate that temperatures could soar in certain periods by up to 6C higher than the norm, while rainfall could be 300% of normal levels.

The probability of the worst-case outcomes coming to pass could not be calculated due to a lack of certainty about what measures will be implemented to combat global warming and how the climate system will respond. This research was described as similar to security threat evaluations or stress tests for financial systems.

Critical Possibility Elements

• Severe Heating: Planetary heating rising well above 4C by 2100 could transpire if international cooperation fails or if vicious cycles like the Amazon basin perishing emit its enormous store of carbon. This would lead to intense and enduring heatwaves and dry spells plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and becoming unstable due to ocean warming. A collapse starting around 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would struggle enormously and water supplies would be fundamentally reshaped," said the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the Arctic and Antarctic melt abruptly, inundating low-lying areas. Unlike the other scenarios, this possibility is already recognized by coastal engineers.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if industrial aerosols is drastically reduced. This counterintuitive effect occurs because pollution particles from fossil fuel combustion block sunlight from warming the ground.

Planning for the Extreme

The severe models could be applied to guide the development of major projects, including new towns, power generation facilities and flood defences. Knowledge about these future hazards could also speed the drive to reduce fossil fuel emissions.

The analysis formulated the extreme models using a blend of observed and historical experience, digital projections and established principles. The possibilities exclude international cascading effects like the agricultural collapse and geopolitical instability.

The project was initiated as part of a national climate resilience programme. Earlier reports have cautioned that not enough attention was being paid to high-consequence, low-probability risks.

Official experts has stated that the UK needs to "become resilient to moderate heating" and examine the threats for severe warming. Previous adaptation plans have been described as being "very weak" by environmental groups.

A government spokesperson said: "Global warming is at the core of our national priorities, both building resilience and transitioning to a clean energy superpower. It is crucial that the UK is ready for the impacts."