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The most severe potential impacts of the climate crisis for the UK have been outlined by researchers, including a scorching 4C increase in average temperatures to a 6.5-foot increase in sea levels. A separate possibility foresees a drop of 6C in temperatures following the failure of crucial Atlantic Ocean currents, which would severely impact farming and energy demand.

Credible Events, Not Guarantees

These impacts, some of which are linked to critical climate thresholds, are considered as low probability but possible. The researchers said that these models plugged a hole in risk assessment that had rendered the UK ill-prepared for catastrophic possibilities.

"The climate extremes we have detailed should not be seen as certainties, but they are credible," said the professor who led the study. "The UK has been making preparations without the frameworks to plan for worst-case scenarios. We've now supplied policymakers what they need to get ready for environmental results they pray never occur, but must not overlook."

A Spectrum of Harsh Climate Scenarios

A further series of dire projections maps the projected severity of extreme weather between now and the end of the century. These suggest that thermometer readings could skyrocket in certain periods by up to 6C higher than average, while rainfall could be 300% of normal levels.

The likelihood of the catastrophic events occurring remains uncertain due to uncertainty about what steps will be implemented to tackle climate change and how the Earth's systems will react. This approach was compared to national security risk assessments or scenario planning for economic stability.

Critical Scenario Details

• 4C Temperature Rise: Global temperatures exceeding 4C by 2100 could transpire if international cooperation breaks down or if vicious cycles like the Amazon rainforest perishing emit its vast reserves of carbon. This would result in severe and lengthy heatwaves and dry spells affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is losing strength and showing signs of collapse due to climate change. A collapse beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and freshwater availability would be completely altered," explained the lead researcher.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in Greenland and Antarctica melt abruptly, flooding coastal cities and towns. Differing from the other scenarios, this threat is already understood by coastal engineers.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because pollution particles from fossil fuel combustion scatter sunlight from reaching the ground.

Preparing for the Worst

These dire projections could be applied to guide the building of critical national infrastructure, for example expanded cities, energy plants and urban drainage systems. Understanding these future hazards could also hasten the push to cut greenhouse gas emissions.

The analysis developed the severe projections using a blend of real-world events, computer simulations and climate physics. The possibilities omit broader worldwide issues including the agricultural collapse and increased conflict.

The research was requested as part of a government’s adaptation planning initiative. Earlier reports have cautioned that too little consideration was being given to high-consequence, low-probability risks.

Official experts has said that the UK needs to "adapt to 2C" and examine the dangers for 4C. Previous adaptation plans have been described as being "very weak" by certain experts.

A government spokesperson said: "Climate change is at the core of our national priorities, both adapting for the future and establishing itself as a renewable energy leader. It is vital that the UK is resilient for the impacts."