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The most severe projected effects of the global heating for the UK have been mapped by scientists, ranging from a searing 4C jump in mean temperatures to a 2-metre rise in ocean levels. A separate possibility foresees a decline of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset food production and energy demand.

Plausible Extremes, Not Forecasts

These effects, some of which are connected to climate tipping points, are considered as low probability but credible. The team stated that these models plugged a hole in forecasting that had rendered the UK unprepared for worst-case results.

"The worst-case scenarios we have detailed should not be seen as certainties, but they are plausible," commented the professor who led the research. "Britain has been formulating policy lacking the methods to test against extreme possibilities. We've now supplied policymakers what they need to plan for climate outcomes they pray never occur, but dare not dismiss."

A Range of Extreme Weather Projections

A further series of dire projections maps the potential extent of severe conditions between now and the year 2100. These show that temperatures could rocket in particular seasons by up to 6C above average, while rainfall could be triple standard measurements.

The likelihood of the worst-case outcomes occurring remains uncertain due to uncertainty about what measures will be enacted to tackle climate change and how the Earth's systems will behave. This approach was compared to defence planning or resilience checks for financial systems.

Major Possibility Elements

• Four-Degree Warming: Planetary heating rising well above 4C by 2100 could happen if international cooperation fails or if vicious cycles like the tropical forests becoming a net carbon source release its huge repository of carbon. This would result in extreme and prolonged heat domes and water shortages hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is weakening and showing signs of collapse due to global heating. A collapse commencing by 2030 would lead to a 6C cooling in the UK. "Farming would be severely challenged and freshwater availability would be completely altered," explained the professor.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions collapse rapidly, inundating coastal cities and towns. Differing from the other scenarios, this threat is already recognized by coastal engineers.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if industrial aerosols is drastically reduced. This paradoxical outcome occurs because aerosol particles from industrial activity reflect solar radiation from warming the ground.

Preparing for the Worst

The worst-case scenarios could be utilized in planning the building of long-term infrastructure, for example housing developments, energy plants and urban drainage systems. Awareness of these climate risks could also hasten the drive to cut carbon pollution.

The analysis created the extreme models using a combination of real-world events, computer simulations and scientific theory. The scenarios omit broader worldwide issues such as the devastation of food supplies and resource wars.

The project was requested as part of a government’s climate resilience programme. Previous assessments have warned that not enough attention was being paid to low‐likelihood but high‐impact risks.

An independent advisory body has recommended that the UK must "adapt to 2C" and assess the threats for four degrees. Past policy documents have been described as being "insufficient" by certain experts.

A national response said: "The climate emergency is at the heart of the country's focus, both building resilience and becoming a renewable energy leader. It is crucial that the UK is ready for the impacts."