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The direst possible consequences of the climate emergency for the UK have been mapped by scientists, ranging from a blistering 4C increase in mean temperatures to a two-metre rise in sea level. Another scenario foresees a plunge of 6C in temperature following the collapse of key Atlantic Ocean currents, which would severely impact agriculture and power requirements.

Credible Outcomes, Not Predictions

These impacts, some of which are linked to climate tipping points, are seen as improbable but credible. The researchers stated that these scenarios filled a gap in forecasting that had left the UK unprepared for worst-case results.

"The severe weather events we have outlined aren’t predictions, but they are credible," said Nigel Arnell who directed the analysis. "The nation has been making preparations lacking the tools to test against worst-case scenarios. We've now provided decision-makers what they need to plan for environmental results they wish to avoid, but must not overlook."

A Suite of Harsh Climate Scenarios

A further series of dire projections maps the potential extent of severe conditions between now and the end of the century. These indicate that temperatures could rocket in certain periods by up to 6C higher than average, while precipitation could be three times standard measurements.

The chance of the worst-case outcomes happening cannot be precisely determined due to unknown factors about what action will be implemented to tackle global heating and how the climate system will react. This analysis was likened to security threat evaluations or stress tests for the banking sector.

Critical Possibility Elements

• Four-Degree Warming: Planetary heating soaring past 4C by 2100 could transpire if emissions cuts collapses or if vicious cycles such as the tropical forests becoming a net carbon source emit its enormous store of carbon. This would cause extreme and prolonged heatwaves and dry spells hitting the UK in summer.
• AMOC Shutdown: A key circulation system, the AMOC, is slowing down and losing stability due to ocean warming. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and freshwater availability would be completely altered," said Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in Greenland and Antarctica collapse rapidly, inundating coastal cities and towns. Unlike the other scenarios, this risk is already understood by infrastructure experts.
• Clean Air Warming: Global averages could also be increased by about 0.75C if airborne particulates is rapidly cleaned up. This unexpected result occurs because aerosol particles from fossil fuel combustion reflect solar radiation from reaching the ground.

Planning for the Unthinkable

These dire projections could be applied to guide the building of critical national infrastructure, for example expanded cities, nuclear power stations and water management networks. Understanding these environmental threats could also speed the push to slash fossil fuel emissions.

The research formulated the extreme models using a blend of observed and historical experience, digital projections and climate physics. The scenarios do not take into account potential global problems such as the agricultural collapse and increased conflict.

The research was commissioned as part of a official adaptation planning initiative. Earlier reports have warned that insufficient focus was being allocated to catastrophic yet improbable risks.

Official experts has said that the UK must "prepare for two degrees of warming" and assess the risks for severe warming. Past policy documents have been described as being "inadequate" by some observers.

An official statement commented: "The climate emergency is at the core of the country's focus, both building resilience and establishing itself as a low-carbon economy. It is essential that the UK is resilient for the impacts."