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The gravest possible consequences of the climate emergency for the UK have been detailed by experts, encompassing a blistering 4C increase in temperatures to a two-metre surge in sea level. An alternative projection predicts a drop of 6C in temperatures following the shutdown of critical Atlantic Ocean currents, which would severely impact farming and power requirements.

Plausible Events, Not Guarantees

These impacts, a number of which are connected to irreversible climate shifts, are considered as improbable but possible. The scientists explained that these projections plugged a hole in risk assessment that had left the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are credible," stated Nigel Arnell who led the analysis. "The UK has been formulating policy in the absence of the tools to test against extreme possibilities. We've now supplied planners what they need to get ready for future conditions they wish to avoid, but can’t afford to ignore."

A Suite of Extreme Weather Scenarios

Another collection of severe models details the possible scale of harsh climate between now and the year 2100. These indicate that thermometer readings could rocket in particular seasons by up to 6C above historical levels, while rainfall could be three times typical amounts.

The probability of the worst-case outcomes occurring remains uncertain due to unknown factors about what steps will be implemented to tackle global heating and how the Earth's systems will react. This analysis was compared to national security risk assessments or stress tests for the banking sector.

Key Possibility Highlights

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could occur if climate action fails or if strong feedback loops such as the Amazon rainforest perishing release its enormous store of carbon. This would result in severe and lengthy heatwaves and droughts hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and showing signs of collapse due to ocean warming. A complete failure commencing by 2030 would lead to a 6C cooling in the UK. "Agriculture would struggle enormously and freshwater availability would be completely altered," said the professor.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica melt abruptly, inundating coastal cities and towns. Differing from the other scenarios, this threat is already recognized by planners.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if airborne particulates is sharply cut. This paradoxical outcome occurs because tiny specks from burning coal block sunlight from reaching the ground.

Planning for the Worst

The severe models could be applied to guide the construction of critical national infrastructure, for example expanded cities, energy plants and water management networks. Awareness of these future hazards could also hasten the transition to slash fossil fuel emissions.

The study created the severe projections using a mix of observed and historical experience, digital projections and climate physics. The possibilities omit international cascading effects like the devastation of food supplies and resource wars.

The project was commissioned as part of a national risk assessment framework. Independent analyses have cautioned that insufficient focus was being paid to low‐likelihood but high‐impact risks.

Official experts has recommended that the UK needs to "adapt to 2C" and assess the risks for severe warming. Previous adaptation plans have been labeled being "insufficient" by environmental groups.

An official statement said: "Climate change is at the core of the country's focus, both adapting for the future and transitioning to a clean energy superpower. It is essential that the UK is prepared for the effects."