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The most severe potential impacts of the climate emergency for the UK have been mapped by scientists, ranging from a searing 4C increase in mean temperatures to a two-metre increase in ocean levels. A separate possibility foresees a decline of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Events, Not Guarantees

These effects, a number of which are associated with irreversible climate shifts, are viewed as low probability but credible. The scientists said that these projections filled a gap in planning that had left the UK unprepared for worst-case results.

"The severe weather events we have mapped aren’t predictions, but they are credible," said the professor who directed the analysis. "Britain has been planning in the absence of the tools to test against worst-case scenarios. We've now given decision-makers what they need to get ready for environmental results they pray never occur, but dare not dismiss."

A Suite of Extreme Weather Possibilities

A second set of worst-case scenarios maps the possible scale of severe conditions between now and the end of the century. These indicate that temperatures could rocket in some months by up to 6C above historical levels, while rainfall could be 300% of normal levels.

The probability of the catastrophic events occurring remains uncertain due to uncertainty about what action will be enacted to tackle global heating and how the Earth's systems will react. This approach was compared to security threat evaluations or resilience checks for financial systems.

Major Scenario Details

• Four-Degree Warming: Worldwide averages rising well above 4C by 2100 could occur if emissions cuts fails or if vicious cycles including the Amazon basin perishing release its enormous store of carbon. This would lead to extreme and prolonged heat domes and dry spells plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the North Atlantic current, is losing strength and showing signs of collapse due to global heating. A complete failure beginning in 2030 would lead to a six-degree temperature drop in the UK. "Crop production would struggle enormously and freshwater availability would be completely altered," noted the professor.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in Greenland and Antarctica disintegrate quickly, flooding coastal cities and towns. Differing from the other scenarios, this threat is already known by infrastructure experts.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if pollution from industry is sharply cut. This paradoxical outcome occurs because tiny specks from burning coal block solar radiation from reaching the ground.

Preparing for the Worst

The severe models could be used to inform the construction of major projects, such as housing developments, nuclear power stations and urban drainage systems. Awareness of these climate risks could also speed the drive to reduce greenhouse gas emissions.

The study formulated the worst-case scenarios using a blend of past data and records, digital projections and climate physics. These outcomes exclude potential global problems including the agricultural collapse and increased conflict.

This work was commissioned as part of a government’s adaptation planning initiative. Earlier reports have warned that not enough attention was being given to catastrophic yet improbable risks.

An independent advisory body has said that the UK needs to "become resilient to moderate heating" and examine the dangers for four degrees. Previous adaptation plans have been criticised as being "inadequate" by some observers.

An official statement said: "Global warming is at the center of our national priorities, both building resilience and establishing itself as a clean energy superpower. It is vital that the UK is ready for the impacts."