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The most severe projected effects of the climate crisis for the UK have been mapped by researchers, including a blistering 4C rise in average temperatures to a 6.5-foot increase in ocean levels. Another scenario predicts a drop of 6C in temperatures following the failure of crucial Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Events, Not Forecasts

These impacts, a number of which are associated with irreversible climate shifts, are viewed as unlikely but possible. The scientists explained that these projections addressed a shortfall in forecasting that had left the UK ill-prepared for worst-case results.

"The worst-case scenarios we have detailed aren’t predictions, but they are plausible," said the lead researcher who led the study. "The UK has been formulating policy without the methods to plan for worst-case scenarios. We've now provided decision-makers what they need to prepare for environmental results they pray never occur, but dare not dismiss."

A Spectrum of Severe Conditions Possibilities

A second set of worst-case scenarios sets out the possible scale of extreme weather between now and the year 2100. These indicate that temperatures could soar in certain periods by up to 6C above average, while rainfall could be 300% of standard measurements.

The likelihood of the worst-case outcomes occurring remains uncertain due to a lack of certainty about what steps will be implemented to combat climate change and how the climate system will respond. This research was described as similar to security threat evaluations or scenario planning for economic stability.

Key Outcome Highlights

• Severe Heating: Global temperatures exceeding 4C by 2100 could transpire if emissions cuts breaks down or if strong feedback loops like the Amazon basin perishing release its vast reserves of carbon. This would lead to intense and enduring heat domes and dry spells affecting the UK in summer.
• AMOC Shutdown: A major ocean current, the North Atlantic current, is weakening and losing stability due to climate change. A full shutdown beginning in 2030 would lead to a 6C cooling in the UK. "Crop production would be severely challenged and water supplies would be fundamentally reshaped," explained the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the Arctic and Antarctic melt abruptly, flooding coastal cities and towns. In contrast to the other scenarios, this possibility is already understood by infrastructure experts.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because tiny specks from industrial activity reflect sunlight from reaching the ground.

Building Resilience Against the Unthinkable

The severe models could be used to inform the development of major projects, including new towns, nuclear power stations and water management networks. Awareness of these climate risks could also hasten the transition to reduce fossil fuel emissions.

The research formulated the extreme models using a blend of observed and historical experience, digital projections and established principles. These outcomes omit potential global problems including the agricultural collapse and geopolitical instability.

The research was requested as part of a national risk assessment framework. Previous assessments have warned that too little consideration was being allocated to high-consequence, low-probability risks.

The government's climate advisors has stated that the UK needs to "become resilient to moderate heating" and examine the risks for 4C. Past policy documents have been described as being "inadequate" by certain experts.

A national response said: "The climate emergency is at the core of this government’s agenda, both building resilience and transitioning to a low-carbon economy. It is crucial that the UK is ready for the effects."