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The direst potential impacts of the global heating for the UK have been mapped by experts, including a blistering 4C increase in average temperatures to a 6.5-foot increase in sea levels. Another scenario envisions a decline of 6C in temperatures following the collapse of critical Atlantic Ocean currents, which would profoundly upset agriculture and energy needs.

Possible Outcomes, Not Predictions

These consequences, some of which are linked to climate tipping points, are considered as improbable but possible. The team said that these projections filled a gap in planning that had rendered the UK unprepared for extreme outcomes.

"The worst-case scenarios we have detailed aren’t predictions, but they are credible," stated the professor who directed the analysis. "The nation has been planning lacking the frameworks to plan for worst-case scenarios. We've now provided decision-makers what they need to prepare for environmental results they wish to avoid, but can’t afford to ignore."

A Suite of Severe Conditions Scenarios

Another collection of dire projections sets out the possible scale of extreme weather between now and the year 2100. These show that temperatures could rocket in particular seasons by up to 6C above the norm, while precipitation could be triple normal levels.

The likelihood of the extreme scenarios happening could not be calculated due to uncertainty about what measures will be enacted to combat climate change and how the Earth's systems will respond. This approach was compared to defence planning or resilience checks for economic stability.

Key Scenario Highlights

• Severe Heating: Planetary heating exceeding 4C by 2100 could occur if climate action fails or if strong feedback loops including the Amazon basin dying emit its vast reserves of carbon. This would lead to intense and enduring heat domes and droughts hitting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is losing strength and losing stability due to global heating. A collapse commencing by 2030 would lead to a six-degree temperature drop in the UK. "Crop production would face immense difficulties and water supplies would be completely altered," noted the lead researcher.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the polar regions collapse rapidly, submerging seaside communities. In contrast to the other scenarios, this possibility is already known by planners.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if pollution from industry is sharply cut. This paradoxical outcome occurs because tiny specks from burning coal reflect solar radiation from warming the ground.

Preparing for the Worst

The severe models could be applied to guide the development of major projects, including expanded cities, power generation facilities and flood defences. Awareness of these future hazards could also accelerate the push to cut greenhouse gas emissions.

The analysis created the worst-case scenarios using a combination of observed and historical experience, computer simulations and scientific theory. The scenarios do not take into account international cascading effects including the agricultural collapse and increased conflict.

This work was commissioned as part of a official adaptation planning initiative. Independent analyses have warned 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 severe warming. Earlier government strategies have been described as being "inadequate" by some observers.

A national response noted: "Climate change is at the heart of the country's focus, both preparing for impacts and becoming a renewable energy leader. It is essential that the UK is resilient for the consequences."