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The most severe possible consequences of the climate crisis for the UK have been detailed by scientists, ranging from a blistering 4C increase in temperatures to a 6.5-foot surge in sea levels. A separate possibility envisions a plunge of 6C in temperature following the failure of critical Atlantic Ocean currents, which would massively disrupt agriculture and power requirements.

Credible Extremes, Not Predictions

These effects, some of which are associated with irreversible climate shifts, are considered as low probability but credible. The researchers said that these scenarios filled a gap in forecasting that had left the UK ill-prepared for catastrophic possibilities.

"The climate extremes we have mapped should not be seen as certainties, but they are credible," said the professor who led the analysis. "The UK has been making preparations without the tools to assess worst-case scenarios. We've now provided decision-makers what they need to prepare for climate outcomes they wish to avoid, but dare not dismiss."

A Suite of Harsh Climate Projections

A second set of worst-case scenarios maps the projected severity of harsh climate between now and the close of the 2100s. These suggest that thermometer readings could rocket in particular seasons by up to 6C above the norm, while rainfall could be three times typical amounts.

The probability of the catastrophic events occurring remains uncertain due to a lack of certainty about what measures will be taken to tackle global heating and how the climate system will behave. This approach was compared to national security risk assessments or stress tests for financial systems.

Key Scenario Details

• Severe Heating: Global temperatures soaring past 4C by 2100 could occur if climate action fails or if strong feedback loops like the tropical forests dying release its huge repository of carbon. This would cause extreme and prolonged heatwaves and dry spells affecting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the AMOC, is losing strength and showing signs of collapse due to global heating. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Agriculture would struggle enormously and water resources would be completely altered," said the lead researcher.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in Greenland and Antarctica disintegrate quickly, submerging low-lying areas. In contrast to the other scenarios, this possibility is already recognized by planners.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if airborne particulates is drastically reduced. This counterintuitive effect occurs because pollution particles from burning coal reflect solar radiation from reaching the ground.

Preparing for the Extreme

The worst-case scenarios could be used to inform the building of long-term infrastructure, such as new towns, energy plants and urban drainage systems. Knowledge about these environmental threats could also accelerate the push to slash carbon pollution.

The analysis created the worst-case scenarios using a blend of past data and records, climate models and established principles. The possibilities exclude broader worldwide issues like the agricultural collapse and increased conflict.

The project was initiated as part of a official climate resilience programme. Independent analyses have warned that not enough attention was being allocated to high-consequence, low-probability risks.

Official experts has recommended that the UK must "adapt to 2C" and examine the threats for severe warming. Earlier government strategies have been criticised as being "insufficient" by environmental groups.

An official statement commented: "Global warming is at the core of this government’s agenda, both building resilience and becoming a low-carbon economy. It is crucial that the UK is resilient for the consequences."