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The most severe possible consequences of the climate crisis for the UK have been detailed by experts, including a blistering 4C rise in mean temperatures to a two-metre surge in ocean levels. Another scenario predicts a decline of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would severely impact farming and power requirements.

Possible Extremes, Not Guarantees

These effects, certain ones are linked to climate tipping points, are viewed as low probability but plausible. The researchers said that these projections plugged a hole in planning that had left the UK unprepared for extreme outcomes.

"The climate extremes we have mapped should not be seen as certainties, but they are plausible," stated the professor who directed the analysis. "The nation has been making preparations lacking the methods to test against worst-case scenarios. We've now supplied planners what they need to get ready for future conditions they wish to avoid, but must not overlook."

A Suite of Extreme Weather Projections

A second set of worst-case scenarios details the possible scale of harsh climate between now and the close of the 2100s. These show that thermometer readings could skyrocket in some months by up to 6C higher than the norm, while rainfall could be triple typical amounts.

The likelihood of the extreme scenarios coming to pass remains uncertain due to unknown factors about what steps will be taken to address global heating and how the climate system will respond. This analysis was likened to national security risk assessments or scenario planning for economic stability.

Major Outcome Elements

• Four-Degree Warming: Global temperatures rising well above 4C by 2100 could occur if climate action fails or if powerful amplifying effects including the tropical forests dying release its vast reserves of carbon. This would lead to severe and lengthy heatwaves and dry spells plaguing the UK in summer.
• Ocean Circulation Failure: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is slowing down and showing signs of collapse due to climate change. A full shutdown commencing by 2030 would lead to a 6C cooling in the UK. "Farming would be severely challenged and water resources would be drastically changed," said the lead researcher.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the Arctic and Antarctic collapse rapidly, submerging seaside communities. Differing from the other scenarios, this possibility is already understood by infrastructure experts.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if industrial aerosols is rapidly cleaned up. This paradoxical outcome occurs because tiny specks from burning coal reflect solar radiation from warming the ground.

Building Resilience Against the Unthinkable

These dire projections could be used to inform the construction of critical national infrastructure, including new towns, energy plants and water management networks. Knowledge about these climate risks could also hasten the drive to reduce fossil fuel emissions.

The study developed the worst-case scenarios using a combination of past data and records, digital projections and scientific theory. These outcomes exclude potential global problems including the global food shortages and increased conflict.

The research was requested as part of a government’s risk assessment framework. Previous assessments have cautioned that too little consideration was being given to high-consequence, low-probability risks.

The government's climate advisors has said that the UK needs to "adapt to 2C" and examine the risks for severe warming. Previous adaptation plans have been described as being "inadequate" by certain experts.

A national response commented: "The climate emergency is at the heart of this government’s agenda, both building resilience and establishing itself as a low-carbon economy. It is crucial that the UK is resilient for the consequences."