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The direst potential impacts of the climate crisis for the UK have been outlined by scientists, encompassing a scorching 4C rise in mean temperatures to a two-metre increase in sea levels. A separate possibility foresees a drop of 6C in temperature following the failure of key Atlantic Ocean currents, which would massively disrupt agriculture and energy needs.

Plausible Extremes, Not Predictions

These effects, some of which are associated with critical climate thresholds, are considered as low probability but credible. The team said that these scenarios plugged a hole in forecasting that had rendered the UK not ready for worst-case results.

"The climate extremes we have mapped aren’t predictions, but they are credible," said Nigel Arnell who led the study. "The nation has been planning in the absence of the frameworks to assess worst-case scenarios. We've now provided planners what they need to get ready for future conditions they hope never happen, but must not overlook."

A Suite of Harsh Climate Scenarios

A further series of worst-case scenarios details the possible scale of harsh climate between now and the year 2100. These indicate that thermometer readings could rocket in some months by up to 6C above the norm, while precipitation could be 300% of normal levels.

The probability of the worst-case outcomes happening remains uncertain due to unknown factors about what action will be implemented to combat climate change and how the climate system will respond. This analysis was described as similar to defence planning or scenario planning for economic stability.

Key Possibility Elements

• 4C Temperature Rise: Planetary heating soaring past 4C by 2100 could occur if emissions cuts fails or if powerful amplifying effects including the Amazon rainforest dying release its huge repository of carbon. This would cause severe and lengthy heatwaves and water shortages affecting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the North Atlantic current, is losing strength and becoming unstable due to ocean warming. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Farming would face immense difficulties and water supplies would be drastically changed," noted Arnell.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in Greenland and Antarctica melt abruptly, flooding low-lying areas. Unlike the other scenarios, this possibility is already known by planners.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if industrial aerosols is rapidly cleaned up. This unexpected result occurs because pollution particles from fossil fuel combustion reflect sunlight from warming the ground.

Building Resilience Against the Worst

The severe models could be utilized in planning the construction of long-term infrastructure, such as new towns, nuclear power stations and urban drainage systems. Understanding these future hazards could also hasten the push to cut greenhouse gas emissions.

The study developed the worst-case scenarios using a blend of observed and historical experience, computer simulations and scientific theory. These outcomes omit potential global problems including the agricultural collapse and increased conflict.

This work was requested as part of a government’s climate resilience programme. Previous assessments have warned that not enough attention was being given to high-consequence, low-probability risks.

Official experts has stated that the UK must "become resilient to moderate heating" and assess the threats for four degrees. Past policy documents have been criticised as being "very weak" by some observers.

A national response commented: "Global warming is at the center of our national priorities, both adapting for the future and becoming a renewable energy leader. It is crucial that the UK is resilient for the effects."