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The gravest potential impacts of the climate emergency for the UK have been mapped by experts, including a searing 4C jump in average temperatures to a 6.5-foot increase in sea levels. Another scenario predicts a drop of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would profoundly upset farming and power requirements.

Credible Extremes, Not Predictions

These consequences, some of which are associated with climate tipping points, are considered as unlikely but plausible. The researchers said that these models addressed a shortfall in planning that had rendered the UK ill-prepared for extreme outcomes.

"The climate extremes we have detailed aren’t predictions, but they are possible," said Nigel Arnell who oversaw the study. "The nation has been planning without the tools to plan for extreme possibilities. We've now provided policymakers what they need to prepare for future conditions they hope never happen, but must not overlook."

A Range of Harsh Climate Scenarios

A further series of worst-case scenarios sets out the potential extent of extreme weather between now and the year 2100. These show that thermometer readings could soar in some months by up to 6C above historical levels, while rainfall could be three times typical amounts.

The chance of the worst-case outcomes coming to pass remains uncertain due to a lack of certainty about what steps will be taken to address global warming and how the climate system will respond. This approach was compared to security threat evaluations or scenario planning for the banking sector.

Key Outcome Details

• Severe Heating: Worldwide averages exceeding 4C by 2100 could happen if climate action breaks down or if powerful amplifying effects like the Amazon basin dying emit its vast reserves of carbon. This would result in intense and enduring heatwaves and dry spells affecting the UK in summer.
• AMOC Shutdown: A major ocean current, the North Atlantic current, is weakening and becoming unstable due to climate change. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Crop production would struggle enormously and freshwater availability would be fundamentally reshaped," noted the professor.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in Greenland and Antarctica disintegrate quickly, submerging low-lying areas. Unlike the other scenarios, this possibility is already known by coastal engineers.
• Clean Air Warming: Global averages could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This paradoxical outcome occurs because pollution particles from burning coal reflect solar radiation from reaching the ground.

Building Resilience Against the Unthinkable

These dire projections could be utilized in planning the construction of critical national infrastructure, including housing developments, energy plants and water management networks. Awareness of these climate risks could also hasten the drive to reduce greenhouse gas emissions.

The research developed the worst-case scenarios using a combination of past data and records, climate models and established principles. The scenarios exclude broader worldwide issues such as the agricultural collapse and increased conflict.

The project was requested as part of a official climate resilience programme. Earlier reports have stated that not enough attention was being paid to catastrophic yet improbable risks.

Official experts has said that the UK must "adapt to 2C" and evaluate the dangers for four degrees. Previous adaptation plans have been criticised as being "very weak" by environmental groups.

An official statement said: "Global warming is at the center of the country's focus, both preparing for impacts and transitioning to a renewable energy leader. It is vital that the UK is resilient for the effects."