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The most severe potential impacts of the climate crisis for the UK have been detailed by researchers, including a searing 4C rise in temperatures to a 6.5-foot surge in sea levels. An alternative projection predicts a decline of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would severely impact food production and power requirements.

Credible Events, Not Guarantees

These consequences, some of which are connected to critical climate thresholds, are viewed as low probability but possible. The team said that these projections addressed a shortfall in risk assessment that had rendered the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are possible," said Nigel Arnell who oversaw the study. "Britain has been making preparations lacking the methods to assess catastrophic outcomes. We've now given decision-makers what they need to prepare for future conditions they wish to avoid, but can’t afford to ignore."

A Spectrum of Extreme Weather Possibilities

A second set of severe models maps the possible scale of severe conditions between now and the year 2100. These show that temperatures could rocket in some months by up to 6C higher than the norm, while precipitation could be triple typical amounts.

The chance of the catastrophic events occurring could not be calculated due to uncertainty about what steps will be enacted to combat global heating and how the climate system will react. This research was likened to national security risk assessments or scenario planning for the banking sector.

Critical Scenario Highlights

• Four-Degree Warming: Worldwide averages exceeding 4C by 2100 could occur if international cooperation fails or if strong feedback loops including the Amazon rainforest dying release its huge repository of carbon. This would lead to severe and lengthy heatwaves and dry spells hitting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is slowing down and becoming unstable due to climate change. A complete failure 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," said the professor.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the polar regions melt abruptly, flooding low-lying areas. Unlike the other scenarios, this possibility is already known by coastal engineers.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if industrial aerosols is drastically reduced. This paradoxical outcome occurs because aerosol particles from burning coal block sunlight from reaching the ground.

Preparing for the Worst

The severe models could be applied to guide the building of major projects, including expanded cities, nuclear power stations and water management networks. Knowledge about these environmental threats could also accelerate the transition to reduce fossil fuel emissions.

The study developed the extreme models using a mix of real-world events, computer simulations and established principles. These outcomes do not take into account potential global problems including the global food shortages and geopolitical instability.

The research was commissioned as part of a national adaptation planning initiative. Independent analyses have warned that insufficient focus was being allocated to high-consequence, low-probability risks.

An independent advisory body has said that the UK needs to "become resilient to moderate heating" and evaluate the threats for severe warming. Previous adaptation plans have been labeled being "very weak" by environmental groups.

An official statement said: "Climate change is at the heart of the country's focus, both adapting for the future and transitioning to a low-carbon economy. It is crucial that the UK is prepared for the impacts."