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The most severe projected effects of the global heating for the UK have been mapped by researchers, including a scorching 4C rise in mean temperatures to a 6.5-foot surge in sea level. Another scenario predicts a drop of 6C in temperature following the failure of crucial Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Credible Events, Not Guarantees

These impacts, a number of which are connected to climate tipping points, are seen as improbable but possible. The team explained that these scenarios plugged a hole in planning that had left the UK ill-prepared for extreme outcomes.

"The severe weather events we have mapped should not be seen as certainties, but they are credible," said Nigel Arnell who led the analysis. "The nation has been formulating policy lacking the methods to test against extreme possibilities. We've now supplied policymakers what they need to get ready for environmental results they pray never occur, but must not overlook."

A Range of Severe Conditions Projections

A further series of worst-case scenarios maps the possible scale of extreme weather between now and the year 2100. These indicate that temperatures could soar in some months by up to 6C higher than average, while rainfall could be three times typical amounts.

The chance of the catastrophic events coming to pass cannot be precisely determined due to uncertainty about what measures will be enacted to combat global heating and how the planet's climate will react. This approach was described as similar to security threat evaluations or resilience checks for the banking sector.

Key Scenario Highlights

• 4C Temperature Rise: Global temperatures soaring past 4C by 2100 could transpire if climate action collapses or if vicious cycles such as the tropical forests dying emit its vast reserves of carbon. This would cause severe and lengthy heatwaves and droughts plaguing the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is losing strength and showing signs of collapse due to ocean warming. A collapse beginning in 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would be severely challenged and water supplies would be drastically changed," explained the lead researcher.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic disintegrate quickly, inundating coastal cities and towns. In contrast to the other scenarios, this threat is already understood by planners.
• Clean Air Warming: Temperatures could also be increased by about 0.75C if industrial aerosols is rapidly cleaned up. This unexpected result occurs because aerosol particles from fossil fuel combustion block solar radiation from reaching the ground.

Building Resilience Against the Worst

The worst-case scenarios could be applied to guide the development of long-term infrastructure, for example expanded cities, power generation facilities and flood defences. Understanding these environmental threats could also speed the drive to slash greenhouse gas emissions.

The analysis created the worst-case scenarios using a blend of observed and historical experience, climate models and climate physics. These outcomes omit potential global problems including the global food shortages and increased conflict.

This work was requested as part of a national adaptation planning initiative. Independent analyses have warned that too little consideration was being given to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "prepare for two degrees of warming" and examine the threats for severe warming. Earlier government strategies have been criticised as being "very weak" by certain experts.

A national response noted: "Climate change is at the core of this government’s agenda, both building resilience and establishing itself as a renewable energy leader. It is vital that the UK is resilient for the effects."