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The gravest 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 rise in sea levels. Another scenario foresees a decline of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would severely impact farming and power requirements.

Credible Outcomes, Not Guarantees

These consequences, some of which are linked to critical climate thresholds, are considered as improbable but credible. The scientists said that these models addressed a shortfall in planning that had rendered the UK ill-prepared for catastrophic possibilities.

"The severe weather events we have mapped aren’t predictions, but they are credible," said Nigel Arnell who oversaw the research. "The UK has been planning without the methods to test against catastrophic outcomes. We've now supplied decision-makers what they need to get ready for future conditions they hope never happen, but can’t afford to ignore."

A Range of Harsh Climate Scenarios

A second set of severe models sets out the projected severity 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 historical levels, while precipitation could be triple typical amounts.

The likelihood of the extreme scenarios occurring cannot be precisely determined due to uncertainty about what measures will be taken to tackle global warming and how the Earth's systems will behave. This research was compared to national security risk assessments or stress tests for economic stability.

Key Scenario Elements

• Four-Degree Warming: Worldwide averages soaring past 4C by 2100 could transpire if emissions cuts breaks down or if powerful amplifying effects such as the Amazon basin dying unleash its vast reserves of carbon. This would lead to intense and enduring heat domes and water shortages affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the North Atlantic current, is slowing down and losing stability due to global heating. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Crop production would face immense difficulties and water resources would be completely altered," explained the lead researcher.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the Arctic and Antarctic melt abruptly, flooding coastal cities and towns. Unlike the other scenarios, this possibility is already recognized by infrastructure experts.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if airborne particulates is rapidly cleaned up. This unexpected result occurs because tiny specks from fossil fuel combustion scatter solar radiation from warming the ground.

Preparing for the Extreme

The severe models could be applied to guide the building of critical national infrastructure, such as new towns, power generation facilities and flood defences. Knowledge about these future hazards could also accelerate the push to slash carbon pollution.

The analysis created the worst-case scenarios using a mix of real-world events, climate models and climate physics. The possibilities omit broader worldwide issues such as the agricultural collapse and geopolitical instability.

This work was requested as part of a national climate resilience programme. Previous assessments have warned that insufficient focus was being given to catastrophic yet improbable risks.

Official experts has recommended that the UK needs to "adapt to 2C" and examine the dangers for 4C. Earlier government strategies have been labeled being "inadequate" by some observers.

A government spokesperson said: "The climate emergency is at the center of this government’s agenda, both building resilience and establishing itself as a renewable energy leader. It is essential that the UK is resilient for the impacts."