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The direst potential impacts of the global heating for the UK have been mapped by experts, ranging from a searing 4C jump in average temperatures to a two-metre increase in ocean levels. An alternative projection predicts a decline of 6C in temperature following the collapse of crucial Atlantic Ocean currents, which would profoundly upset farming and energy needs.

Plausible Outcomes, Not Guarantees

These effects, certain ones are connected to climate tipping points, are viewed as low probability but possible. The team stated that these projections filled a gap in planning that had rendered the UK ill-prepared for worst-case results.

"The severe weather events we have detailed are not forecasts, but they are possible," stated Nigel Arnell who oversaw the research. "Britain has been planning lacking the methods to plan for worst-case scenarios. We've now given planners what they need to get ready for future conditions they pray never occur, but dare not dismiss."

A Range of Extreme Weather Scenarios

Another collection of dire projections details the possible scale of extreme weather between now and the year 2100. These indicate that temperatures could soar in particular seasons by up to 6C above the norm, while rainfall could be 300% of standard measurements.

The probability of the worst-case outcomes happening remains uncertain due to unknown factors about what measures will be implemented to address climate change and how the planet's climate will behave. This approach was compared to national security risk assessments or scenario planning for financial systems.

Critical Possibility Elements

• Four-Degree Warming: Planetary heating rising well above 4C by 2100 could happen if emissions cuts collapses or if vicious cycles such as the Amazon basin dying release its huge repository of carbon. This would result in extreme and prolonged heat domes and water shortages plaguing the UK in summer.
• Atlantic Current Collapse: A major ocean current, the North Atlantic current, is slowing down and becoming unstable due to global heating. A full shutdown commencing by 2030 would lead to a 6C cooling in the UK. "Farming would struggle enormously and freshwater availability would be completely altered," explained the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the Arctic and Antarctic collapse rapidly, flooding seaside communities. In contrast to the other scenarios, this possibility is already understood by planners.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if pollution from industry is drastically reduced. This unexpected result occurs because tiny specks from burning coal block sunlight from warming the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be used to inform the construction of long-term infrastructure, for example new towns, power generation facilities and flood defences. Knowledge about these future hazards could also speed the drive to cut fossil fuel emissions.

The study developed the extreme models using a mix of observed and historical experience, climate models and climate physics. The scenarios do not take into account broader worldwide issues like the global food shortages and geopolitical instability.

The project was requested as part of a official adaptation planning initiative. Previous assessments have cautioned that too little consideration was being allocated to low‐likelihood but high‐impact risks.

Official experts has stated that the UK must "become resilient to moderate heating" and assess the threats for severe warming. Past policy documents have been described as being "insufficient" by some observers.

A national response noted: "Global warming is at the core of this government’s agenda, both preparing for impacts and establishing itself as a renewable energy leader. It is crucial that the UK is ready for the impacts."