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The direst projected effects of the global heating for the UK have been detailed by scientists, ranging from a searing 4C jump in mean temperatures to a 2-metre rise in sea levels. Another scenario envisions a plunge of 6C in temperature following the failure of key Atlantic Ocean currents, which would severely impact farming and energy needs.

Plausible Outcomes, Not Forecasts

These effects, some of which are connected to irreversible climate shifts, are seen as low probability but credible. The team explained that these projections plugged a hole in forecasting that had left the UK not ready for worst-case results.

"The climate extremes we have detailed aren’t predictions, but they are credible," stated the lead researcher who led the study. "The nation has been making preparations without the tools to plan for worst-case scenarios. We've now provided policymakers what they need to get ready for climate outcomes they hope never happen, but must not overlook."

A Suite of Extreme Weather Possibilities

A second set of dire projections maps the projected severity of extreme weather between now and the year 2100. These suggest that thermometer readings could skyrocket in particular seasons by up to 6C above the norm, while rainfall could be 300% of typical amounts.

The chance of the catastrophic events happening cannot be precisely determined due to uncertainty about what steps will be taken to combat global heating and how the Earth's systems will behave. This research was likened to security threat evaluations or scenario planning for economic stability.

Key Possibility Highlights

• 4C Temperature Rise: Global temperatures rising well above 4C by 2100 could happen if climate action collapses or if strong feedback loops like the Amazon rainforest dying emit its enormous store of carbon. This would lead to severe and lengthy heatwaves and droughts hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is slowing down and showing signs of collapse due to climate change. A complete failure beginning in 2030 would lead to a 6C cooling in the UK. "Agriculture would struggle enormously and water supplies would be drastically changed," explained Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the polar regions collapse rapidly, flooding coastal cities and towns. Unlike the other scenarios, this threat is already known by coastal engineers.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if airborne particulates is drastically reduced. This counterintuitive effect occurs because aerosol particles from industrial activity reflect sunlight from warming the ground.

Planning for the Worst

The severe models could be utilized in planning the construction of long-term infrastructure, such as new towns, nuclear power stations and flood defences. Knowledge about these climate risks could also accelerate the drive to cut carbon pollution.

The analysis developed the extreme models using a combination of past data and records, climate models and established principles. These outcomes omit broader worldwide issues such as the agricultural collapse and geopolitical instability.

This work was commissioned as part of a official climate resilience programme. Independent analyses have cautioned that insufficient focus was being given to catastrophic yet improbable risks.

Official experts has recommended that the UK must "adapt to 2C" and evaluate the threats for severe warming. Past policy documents have been described as being "very weak" by certain experts.

A government spokesperson said: "Global warming is at the heart of the country's focus, both building resilience and establishing itself as a clean energy superpower. It is essential that the UK is resilient for the impacts."