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The gravest potential impacts of the climate crisis for the UK have been mapped by experts, including a blistering 4C jump in temperatures to a 2-metre increase in sea level. An alternative projection envisions a plunge of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset farming and power requirements.

Credible Outcomes, Not Predictions

These impacts, some of which are associated with climate tipping points, are seen as improbable but possible. The scientists stated that these models plugged a hole in risk assessment that had left the UK unprepared for worst-case results.

"The severe weather events we have outlined aren’t predictions, but they are credible," said Nigel Arnell who directed the study. "The UK has been formulating policy in the absence of the frameworks to plan for catastrophic outcomes. We've now provided decision-makers what they need to get ready for environmental results they hope never happen, but must not overlook."

A Range of Harsh Climate Scenarios

A further series of dire projections details the possible scale of harsh climate between now and the end of the century. These indicate that thermometer readings could rocket in particular seasons by up to 6C above the norm, while precipitation could be 300% of normal levels.

The likelihood of the extreme scenarios coming to pass could not be calculated due to unknown factors about what measures will be taken to address global heating and how the Earth's systems will respond. This analysis was compared to national security risk assessments or resilience checks for economic stability.

Major Scenario Elements

• Four-Degree Warming: Global temperatures rising well above 4C by 2100 could occur if climate action collapses or if powerful amplifying effects including the Amazon basin becoming a net carbon source unleash its enormous store 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 Atlantic meridional overturning circulation (Amoc), is weakening and showing signs of collapse due to ocean warming. A collapse commencing by 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would be severely challenged and water supplies would be drastically changed," explained the professor.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions melt abruptly, submerging coastal cities and towns. Unlike the other scenarios, this possibility is already recognized by infrastructure experts.
• Aerosol Effect: Temperatures could also be pushed higher by about 0.75C if industrial aerosols is sharply cut. This unexpected result occurs because aerosol particles from industrial activity block sunlight from warming the ground.

Building Resilience Against the Extreme

The worst-case scenarios could be used to inform the construction of critical national infrastructure, including housing developments, nuclear power stations and flood defences. Understanding these future hazards could also speed the transition to reduce carbon pollution.

The analysis formulated the severe projections using a blend of real-world events, computer simulations and scientific theory. The scenarios do not take into account potential global problems like the global food shortages and increased conflict.

The research was requested as part of a government’s climate resilience programme. Earlier reports have warned that insufficient focus was being paid to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK must "prepare for two degrees of warming" and evaluate the risks for four degrees. Past policy documents have been criticised as being "very weak" by certain experts.

An official statement noted: "The climate emergency is at the heart of this government’s agenda, both adapting for the future and becoming a clean energy superpower. It is crucial that the UK is prepared for the consequences."