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The most severe possible consequences of the global heating for the UK have been detailed by experts, including a searing 4C jump in mean temperatures to a two-metre surge in sea level. An alternative projection predicts a decline of 6C in temperatures following the failure of crucial Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Credible Outcomes, Not Forecasts

These impacts, a number of which are linked to climate tipping points, are seen as low probability but possible. The scientists explained that these scenarios plugged a hole in forecasting that had rendered the UK unprepared for extreme outcomes.

"The severe weather events we have mapped should not be seen as certainties, but they are possible," stated Nigel Arnell who oversaw the study. "The nation has been planning without the tools to test against catastrophic outcomes. We've now supplied decision-makers what they need to plan for future conditions they wish to avoid, but must not overlook."

A Spectrum of Harsh Climate Scenarios

A second set of dire projections maps the projected severity of severe conditions between now and the end of the century. These show that temperatures could rocket in some months by up to 6C above the norm, while rainfall could be triple typical amounts.

The likelihood of the catastrophic events occurring cannot be precisely determined due to uncertainty about what steps will be enacted to address global warming and how the Earth's systems will respond. This approach was compared to national security risk assessments or resilience checks for financial systems.

Critical Outcome Details

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could happen if climate action fails or if vicious cycles including the Amazon basin becoming a net carbon source unleash its huge repository of carbon. This would result in intense and enduring heat domes and dry spells hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the North Atlantic current, is weakening and losing stability due to global heating. A complete failure commencing by 2030 would lead to a 6C cooling in the UK. "Crop production would be severely challenged and water resources would be drastically changed," explained the lead researcher.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the Arctic and Antarctic melt abruptly, submerging coastal cities and towns. Differing from the other scenarios, this possibility is already known by coastal engineers.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if airborne particulates is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from industrial activity reflect sunlight from warming the ground.

Planning for the Worst

These dire projections could be used to inform the development of critical national infrastructure, such as new towns, power generation facilities and flood defences. Awareness of these future hazards could also accelerate the drive to reduce greenhouse gas emissions.

The study formulated the worst-case scenarios using a blend of real-world events, climate models and scientific theory. The scenarios do not take into account potential global problems like the global food shortages and increased conflict.

This work was requested as part of a national climate resilience programme. Earlier reports have stated that not enough attention was being allocated to catastrophic yet improbable risks.

The government's climate advisors has said that the UK must "prepare for two degrees of warming" and examine the risks for severe warming. Past policy documents have been labeled being "inadequate" by certain experts.

An official statement commented: "Global warming is at the heart of our national priorities, both adapting for the future and becoming a low-carbon economy. It is crucial that the UK is resilient for the impacts."