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The gravest potential impacts of the climate crisis for the UK have been mapped by scientists, encompassing a searing 4C jump in temperatures to a 6.5-foot surge in sea levels. Another scenario envisions a drop of 6C in temperature following the collapse of key Atlantic Ocean currents, which would profoundly upset farming and power requirements.

Possible Events, Not Guarantees

These effects, a number of which are associated with irreversible climate shifts, are seen as improbable but plausible. The researchers stated that these scenarios addressed a shortfall in forecasting that had rendered the UK unprepared for worst-case results.

"The climate extremes we have detailed aren’t predictions, but they are credible," commented Nigel Arnell who oversaw the research. "The nation has been planning in the absence of the methods to assess worst-case scenarios. We've now supplied policymakers what they need to prepare for environmental results they hope never happen, but must not overlook."

A Spectrum of Extreme Weather Scenarios

Another collection of worst-case scenarios details the potential extent of severe conditions between now and the end of the century. These indicate that thermometer readings could rocket in particular seasons by up to 6C above historical levels, while precipitation could be 300% of normal levels.

The probability of the worst-case outcomes happening cannot be precisely determined due to uncertainty about what measures will be implemented to address global heating and how the Earth's systems will respond. This approach was likened to national security risk assessments or resilience checks for the banking sector.

Key Possibility Highlights

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could happen if emissions cuts breaks down or if strong feedback loops like the Amazon basin becoming a net carbon source release its huge repository of carbon. This would lead to intense and enduring heatwaves and water shortages plaguing the UK in summer.
• AMOC Shutdown: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is slowing down and becoming unstable due to ocean warming. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and freshwater availability would be fundamentally reshaped," said the lead researcher.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions melt abruptly, flooding coastal cities and towns. Differing from the other scenarios, this possibility is already recognized by infrastructure experts.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because tiny specks from fossil fuel combustion scatter solar radiation from reaching the ground.

Building Resilience Against the Worst

The worst-case scenarios could be utilized in planning the development of major projects, including new towns, energy plants and urban drainage systems. Awareness of these environmental threats could also speed the push to slash carbon pollution.

The analysis developed the worst-case scenarios using a blend of past data and records, digital projections and climate physics. The possibilities exclude potential global problems such as the devastation of food supplies and resource wars.

The research was commissioned as part of a government’s climate resilience programme. Earlier reports have warned that not enough attention was being given to catastrophic yet improbable risks.

The government's climate advisors has said that the UK needs to "become resilient to moderate heating" and assess the dangers for severe warming. Earlier government strategies have been criticised as being "very weak" by some observers.

A government spokesperson said: "The climate emergency is at the center of this government’s agenda, both building resilience and becoming a clean energy superpower. It is crucial that the UK is resilient for the impacts."