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The gravest projected effects of the global heating for the UK have been outlined by scientists, ranging from a scorching 4C jump in temperatures to a 2-metre rise in sea level. Another scenario envisions a plunge of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would severely impact farming and energy demand.

Plausible Extremes, Not Predictions

These impacts, a number of which are linked to climate tipping points, are viewed as unlikely but possible. The researchers said that these scenarios addressed a shortfall in forecasting that had rendered the UK unprepared for extreme outcomes.

"The severe weather events we have mapped are not forecasts, but they are possible," said Nigel Arnell who led the study. "Britain has been formulating policy in the absence of the methods to assess catastrophic outcomes. We've now provided decision-makers what they need to get ready for future conditions they pray never occur, but can’t afford to ignore."

A Range of Severe Conditions Possibilities

A further series of dire projections sets out the potential extent 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 probability of the extreme scenarios occurring could not be calculated due to uncertainty about what measures will be enacted to combat climate change and how the climate system will respond. This analysis was compared to national security risk assessments or stress tests for the banking sector.

Critical Outcome Highlights

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could transpire if emissions cuts fails or if strong feedback loops including the Amazon basin becoming a net carbon source unleash its enormous store of carbon. This would cause extreme and prolonged heat domes and dry spells affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is weakening and showing signs of collapse due to ocean warming. A full shutdown commencing by 2030 would lead to a 6C cooling in the UK. "Farming would face immense difficulties and water resources would be drastically changed," explained the lead researcher.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the polar regions melt abruptly, flooding coastal cities and towns. Unlike the other scenarios, this possibility is already known by infrastructure experts.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because pollution particles from fossil fuel combustion reflect solar radiation from warming the ground.

Building Resilience Against the Worst

The severe models could be used to inform the building of critical national infrastructure, for example housing developments, energy plants and flood defences. Knowledge about these climate risks could also accelerate the transition to slash carbon pollution.

The analysis formulated the extreme models using a blend of past data and records, digital projections and scientific theory. These outcomes exclude broader worldwide issues like the devastation of food supplies and increased conflict.

The project was initiated as part of a government’s climate resilience programme. Previous assessments have cautioned that insufficient focus was being allocated to high-consequence, low-probability risks.

The government's climate advisors has said that the UK needs to "become resilient to moderate heating" and examine the dangers for severe warming. Earlier government strategies have been described as being "inadequate" by certain experts.

An official statement said: "Global warming is at the heart of the country's focus, both preparing for impacts and transitioning to a clean energy superpower. It is essential that the UK is ready for the effects."