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The most severe potential impacts of the climate crisis for the UK have been mapped by researchers, ranging from a scorching 4C rise in average temperatures to a 6.5-foot increase in sea level. Another scenario foresees a decline of 6C in temperature following the failure of critical Atlantic Ocean currents, which would severely impact farming and energy demand.

Plausible Events, Not Guarantees

These effects, a number of which are associated with critical climate thresholds, are viewed as low probability but possible. The scientists stated that these scenarios addressed a shortfall in risk assessment that had rendered the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are credible," commented Nigel Arnell who oversaw the study. "The nation has been planning in the absence of the methods to assess extreme possibilities. We've now given decision-makers what they need to prepare for environmental results they hope never happen, but must not overlook."

A Range of Severe Conditions Projections

A second set of worst-case scenarios maps the potential extent of extreme weather between now and the end of the century. These show that thermometer readings could skyrocket in certain periods by up to 6C higher than historical levels, while rainfall could be three times standard measurements.

The chance of the catastrophic events occurring remains uncertain due to uncertainty about what steps will be taken to address climate change and how the Earth's systems will behave. This approach was likened to security threat evaluations or scenario planning for the banking sector.

Major Scenario Details

• 4C Temperature Rise: Global temperatures exceeding 4C by 2100 could happen if climate action breaks down or if vicious cycles including the Amazon rainforest becoming a net carbon source unleash its enormous store of carbon. This would lead to severe and lengthy heatwaves and water shortages affecting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the North Atlantic current, is losing strength and losing stability due to climate change. A complete failure beginning in 2030 would lead to a drastic cooling in the UK. "Farming would be severely challenged and water supplies would be completely altered," said Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in Greenland and Antarctica melt abruptly, inundating seaside communities. In contrast to the other scenarios, this threat is already understood by infrastructure experts.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This paradoxical outcome occurs because pollution particles from fossil fuel combustion reflect solar radiation from reaching the ground.

Planning for the Extreme

The worst-case scenarios could be utilized in planning the building of major projects, for example expanded cities, energy plants and urban drainage systems. Awareness of these future hazards could also accelerate the drive to cut carbon pollution.

The study formulated the severe projections using a mix of real-world events, climate models and climate physics. The scenarios do not take into account potential global problems including the global food shortages and geopolitical instability.

This work was commissioned as part of a national risk assessment framework. Previous assessments have stated that insufficient focus was being given to low‐likelihood but high‐impact risks.

An independent advisory body has recommended that the UK needs to "become resilient to moderate heating" and evaluate the risks for 4C. Earlier government strategies have been criticised as being "insufficient" by some observers.

An official statement noted: "Global warming is at the core of the country's focus, both adapting for the future and establishing itself as a low-carbon economy. It is crucial that the UK is prepared for the effects."