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The most severe potential impacts of the climate crisis for the UK have been detailed by researchers, including a searing 4C jump in mean temperatures to a two-metre rise in sea level. An alternative projection foresees a decline of 6C in temperature following the failure of key Atlantic Ocean currents, which would massively disrupt farming and energy needs.

Credible Outcomes, Not Guarantees

These impacts, some of which are connected to critical climate thresholds, are seen as low probability but possible. The scientists said that these scenarios plugged a hole in risk assessment that had rendered the UK unprepared for worst-case results.

"The worst-case scenarios we have outlined aren’t predictions, but they are credible," commented Nigel Arnell who directed the study. "The nation has been formulating policy lacking the tools to plan for worst-case scenarios. We've now given decision-makers what they need to plan for climate outcomes they wish to avoid, but can’t afford to ignore."

A Suite of Extreme Weather Projections

A further series of worst-case scenarios details the potential extent of severe conditions between now and the close of the 2100s. These show that temperatures could rocket in particular seasons by up to 6C above average, while rainfall could be 300% of normal levels.

The chance of the extreme scenarios happening remains uncertain due to uncertainty about what action will be taken to address global warming and how the planet's climate will react. This approach was compared to defence planning or resilience checks for economic stability.

Major Possibility Details

• Four-Degree Warming: Global temperatures soaring past 4C by 2100 could happen if international cooperation breaks down or if strong feedback loops like the tropical forests dying emit its huge repository of carbon. This would result in severe and lengthy heatwaves and droughts affecting the UK in summer.
• Ocean Circulation Failure: A major ocean current, the North Atlantic current, is weakening and becoming unstable due to global heating. A collapse beginning in 2030 would lead to a six-degree temperature drop in the UK. "Crop production would face immense difficulties and freshwater availability would be fundamentally reshaped," noted the lead researcher.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in the polar regions disintegrate quickly, submerging coastal cities and towns. Unlike the other scenarios, this risk is already recognized by planners.
• Clean Air Warming: Global averages could also be increased by about 0.75C if airborne particulates is sharply cut. This counterintuitive effect occurs because aerosol particles from industrial activity reflect solar radiation from warming the ground.

Planning for the Extreme

The worst-case scenarios could be used to inform the construction of long-term infrastructure, such as new towns, power generation facilities and flood defences. Knowledge about these future hazards could also hasten the drive to cut greenhouse gas emissions.

The study formulated the severe projections using a combination of past data and records, climate models and climate physics. The possibilities do not take into account potential global problems like the devastation of food supplies and resource wars.

The research was commissioned as part of a government’s climate resilience programme. Independent analyses have stated that too little consideration was being given to high-consequence, low-probability risks.

Official experts has recommended that the UK must "become resilient to moderate heating" and evaluate the threats for 4C. Previous adaptation plans have been described as being "very weak" by certain experts.

An official statement noted: "Global warming is at the heart of our national priorities, both preparing for impacts and establishing itself as a low-carbon economy. It is essential that the UK is prepared for the effects."