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The most severe possible consequences of the climate crisis for the UK have been detailed by researchers, including a searing 4C rise in average temperatures to a two-metre surge in sea level. An alternative projection foresees a decline of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would profoundly upset farming and energy needs.

Possible Outcomes, Not Guarantees

These effects, some of which are linked to critical climate thresholds, are viewed as low probability but credible. The researchers stated that these scenarios filled a gap in forecasting that had left the UK ill-prepared for extreme outcomes.

"The climate extremes we have mapped aren’t predictions, but they are credible," said Nigel Arnell who oversaw the research. "The nation has been planning in the absence of the tools to assess extreme possibilities. We've now supplied planners what they need to prepare for future conditions they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Projections

A further series of worst-case scenarios sets out the possible scale of harsh climate between now and the year 2100. These suggest that temperatures could rocket in certain periods by up to 6C above historical levels, while precipitation could be triple standard measurements.

The likelihood of the extreme scenarios occurring cannot be precisely determined due to a lack of certainty about what steps will be taken to tackle climate change and how the climate system will react. This research was described as similar to defence planning or scenario planning for economic stability.

Key Outcome Highlights

• Severe Heating: Global temperatures exceeding 4C by 2100 could happen if climate action breaks down or if vicious cycles such as the tropical forests becoming a net carbon source emit its huge repository of carbon. This would cause intense and enduring heatwaves and water shortages affecting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is slowing down and becoming unstable due to global heating. A full shutdown beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would be severely challenged and freshwater availability would be drastically changed," explained the lead researcher.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in Greenland and Antarctica melt abruptly, flooding coastal cities and towns. In contrast to the other scenarios, this threat is already recognized by planners.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if industrial aerosols is drastically reduced. This unexpected result occurs because tiny specks from fossil fuel combustion block sunlight from warming the ground.

Planning for the Unthinkable

The severe models could be used to inform the construction of long-term infrastructure, including housing developments, nuclear power stations and water management networks. Knowledge about these climate risks could also accelerate the transition to reduce greenhouse gas emissions.

The research created the extreme models using a combination of past data and records, digital projections and established principles. These outcomes do not take into account international cascading effects like the agricultural collapse and geopolitical instability.

The project was commissioned as part of a official adaptation planning initiative. Independent analyses have stated that too little consideration was being paid to high-consequence, low-probability risks.

An independent advisory body has said that the UK needs to "adapt to 2C" and examine the threats for 4C. Earlier government strategies have been labeled being "insufficient" by some observers.

A government spokesperson commented: "The climate emergency is at the center of this government’s agenda, both adapting for the future and establishing itself as a renewable energy leader. It is crucial that the UK is prepared for the impacts."