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The most severe potential impacts of the climate crisis for the UK have been detailed by researchers, including a searing 4C rise in average temperatures to a two-metre increase in sea levels. An alternative projection envisions a plunge of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would massively disrupt agriculture and power requirements.

Possible Extremes, Not Predictions

These impacts, some of which are connected to critical climate thresholds, are seen as low probability but possible. The researchers explained that these projections filled a gap in risk assessment that had left the UK not ready for worst-case results.

"The climate extremes we have outlined are not forecasts, but they are plausible," commented Nigel Arnell who oversaw the research. "The UK has been making preparations in the absence of the methods to test against worst-case scenarios. We've now given planners what they need to get ready for climate outcomes they wish to avoid, but dare not dismiss."

A Range of Severe Conditions Scenarios

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 temperatures could rocket in particular seasons by up to 6C higher than historical levels, while rainfall could be triple normal levels.

The probability of the catastrophic events occurring cannot be precisely determined due to a lack of certainty about what measures will be enacted to combat global heating and how the climate system will behave. This approach was likened to defence planning or stress tests for the banking sector.

Major Outcome Details

• 4C Temperature Rise: Worldwide averages exceeding 4C by 2100 could transpire if international cooperation collapses or if powerful amplifying effects such as the Amazon rainforest becoming a net carbon source release its enormous store of carbon. This would lead to extreme and prolonged heat domes and water shortages hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is weakening and showing signs of collapse due to ocean warming. A collapse commencing by 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.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic collapse rapidly, submerging coastal cities and towns. In contrast to the other scenarios, this risk is already understood by infrastructure experts.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if airborne particulates is rapidly cleaned up. This paradoxical outcome occurs because pollution particles from industrial activity reflect sunlight from reaching the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be used to inform the construction of critical national infrastructure, such as expanded cities, nuclear power stations and urban drainage systems. Knowledge about these climate risks could also speed the push to slash carbon pollution.

The study created the extreme models using a blend of real-world events, climate models and established principles. These outcomes do not take into account broader worldwide issues like the global food shortages and increased conflict.

This work was requested as part of a government’s adaptation planning initiative. Previous assessments have stated that not enough attention was being given to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "adapt to 2C" and evaluate the risks for severe warming. Earlier government strategies have been criticised as being "inadequate" by environmental groups.

A government spokesperson commented: "The climate emergency is at the heart of this government’s agenda, both adapting for the future and transitioning to a clean energy superpower. It is essential that the UK is ready for the consequences."