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The most severe projected effects of the climate crisis for the UK have been mapped by scientists, including a scorching 4C rise in mean temperatures to a two-metre surge in sea levels. An alternative projection envisions a decline of 6C in temperatures following the failure of crucial Atlantic Ocean currents, which would severely impact agriculture and energy demand.

Possible Events, Not Guarantees

These consequences, some of which are linked to irreversible climate shifts, are viewed as improbable but plausible. The scientists said that these projections addressed a shortfall in risk assessment that had left the UK unprepared for extreme outcomes.

"The climate extremes we have mapped should not be seen as certainties, but they are possible," commented Nigel Arnell who led the research. "The nation has been formulating policy lacking the methods to test against catastrophic outcomes. We've now supplied decision-makers what they need to get ready for future conditions they pray never occur, but can’t afford to ignore."

A Range of Harsh Climate Projections

A second set of dire projections details the potential extent of extreme weather between now and the close of the 2100s. These show that temperatures could soar in some months by up to 6C above historical levels, while rainfall could be three times typical amounts.

The likelihood of the catastrophic events occurring cannot be precisely determined due to unknown factors about what action will be taken to tackle global warming and how the climate system will respond. This approach was described as similar to security threat evaluations or stress tests for the banking sector.

Critical Possibility Elements

• Severe Heating: Planetary heating exceeding 4C by 2100 could occur if climate action collapses or if powerful amplifying effects including the Amazon rainforest dying emit its vast reserves of carbon. This would result in extreme and prolonged heatwaves and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is weakening and losing stability due to ocean warming. A full shutdown beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and water supplies would be drastically changed," said the professor.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the polar regions collapse rapidly, submerging low-lying areas. Unlike the other scenarios, this threat is already recognized by planners.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if airborne particulates is rapidly cleaned up. This paradoxical outcome occurs because pollution particles from industrial activity block solar radiation from reaching the ground.

Building Resilience Against the Extreme

The severe models could be used to inform the construction of long-term infrastructure, including housing developments, nuclear power stations and urban drainage systems. Awareness of these environmental threats could also accelerate the drive to reduce carbon pollution.

The research created the worst-case scenarios using a combination of real-world events, digital projections and scientific theory. These outcomes omit broader worldwide issues like the devastation of food supplies and resource wars.

The research was commissioned as part of a official climate resilience programme. Previous assessments have warned that not enough attention was being paid to high-consequence, low-probability risks.

Official experts has recommended that the UK must "adapt to 2C" and examine the threats for 4C. Past policy documents have been described as being "very weak" by certain experts.

An official statement commented: "The climate emergency is at the core of the country's focus, both preparing for impacts and establishing itself as a low-carbon economy. It is essential that the UK is prepared for the consequences."