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The direst potential impacts of the climate crisis for the UK have been detailed by researchers, including a scorching 4C rise in mean temperatures to a 6.5-foot surge in sea level. An alternative projection foresees a plunge of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would profoundly upset agriculture and energy demand.

Possible Events, Not Predictions

These impacts, a number of which are associated with critical climate thresholds, are seen as unlikely but plausible. The researchers explained that these projections plugged a hole in risk assessment that had left the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are credible," said Nigel Arnell who directed the analysis. "The UK has been formulating policy in the absence of the tools to plan for worst-case scenarios. We've now given policymakers what they need to plan for environmental results they pray never occur, but can’t afford to ignore."

A Spectrum of Severe Conditions Possibilities

A further series of dire projections details the projected severity of extreme weather between now and the close of the 2100s. These show that thermometer readings could skyrocket in some months by up to 6C above average, while rainfall could be triple normal levels.

The chance of the catastrophic events happening cannot be precisely determined due to unknown factors about what action will be enacted to tackle global heating and how the planet's climate will respond. This research was described as similar to defence planning or stress tests for economic stability.

Major Possibility Highlights

• 4C Temperature Rise: Worldwide averages exceeding 4C by 2100 could transpire if emissions cuts collapses or if strong feedback loops such as the Amazon rainforest dying emit its vast reserves of carbon. This would lead to extreme and prolonged heatwaves and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is slowing down and losing stability due to climate change. A complete failure starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and water supplies would be drastically changed," explained Arnell.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in Greenland and Antarctica collapse rapidly, flooding coastal cities and towns. Differing from the other scenarios, this possibility is already understood by coastal engineers.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if pollution from industry is sharply cut. This unexpected result occurs because pollution particles from fossil fuel combustion block solar radiation from reaching the ground.

Building Resilience Against the Worst

The worst-case scenarios could be used to inform the building of critical national infrastructure, such as new towns, nuclear power stations and urban drainage systems. Awareness of these climate risks could also accelerate the drive to slash carbon pollution.

The research created the extreme models using a blend of real-world events, digital projections and established principles. These outcomes exclude broader worldwide issues such as the agricultural collapse and resource wars.

This work was initiated as part of a national climate resilience programme. Independent analyses have stated that too little consideration was being given to high-consequence, low-probability risks.

An independent advisory body has recommended that the UK needs to "become resilient to moderate heating" and assess the threats for severe warming. Past policy documents have been criticised as being "insufficient" by environmental groups.

A government spokesperson said: "Climate change is at the heart of our national priorities, both preparing for impacts and establishing itself as a low-carbon economy. It is crucial that the UK is resilient for the consequences."