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The direst potential impacts of the global heating for the UK have been detailed by researchers, encompassing a scorching 4C increase in temperatures to a two-metre increase in sea level. An alternative projection foresees a plunge of 6C in temperatures following the collapse of crucial Atlantic Ocean currents, which would massively disrupt farming and energy needs.

Credible Outcomes, Not Forecasts

These consequences, a number of which are connected to critical climate thresholds, are viewed as improbable but credible. The researchers stated that these scenarios plugged a hole in forecasting that had left the UK unprepared for catastrophic possibilities.

"The climate extremes we have detailed aren’t predictions, but they are possible," commented the professor who oversaw the analysis. "The nation has been formulating policy without the methods to test against catastrophic outcomes. We've now provided policymakers what they need to prepare for future conditions they hope never happen, but can’t afford to ignore."

A Suite of Extreme Weather Projections

A second set of severe models maps the potential extent of severe conditions between now and the year 2100. These indicate that thermometer readings could soar in certain periods by up to 6C above the norm, while precipitation could be 300% of standard measurements.

The chance of the worst-case outcomes coming to pass cannot be precisely determined due to a lack of certainty about what steps will be enacted to combat climate change and how the planet's climate will respond. This research was compared to national security risk assessments or stress tests for economic stability.

Key Scenario Details

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could occur if emissions cuts breaks down or if strong feedback loops such as the tropical forests becoming a net carbon source unleash its huge repository of carbon. This would result in extreme and prolonged heatwaves and droughts plaguing the UK in summer.
• AMOC Shutdown: A major ocean current, the North Atlantic current, is weakening and showing signs of collapse 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 water supplies would be drastically changed," noted Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in Greenland and Antarctica collapse rapidly, submerging low-lying areas. Unlike the other scenarios, this threat is already understood by planners.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if industrial aerosols is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from burning coal block solar radiation from reaching the ground.

Planning for the Unthinkable

The worst-case scenarios could be used to inform the construction of critical national infrastructure, for example new towns, energy plants and water management networks. Understanding these climate risks could also accelerate the transition to reduce carbon pollution.

The research developed the worst-case scenarios using a mix of observed and historical experience, climate models and scientific theory. The scenarios exclude potential global problems including the agricultural collapse and increased conflict.

The project was requested as part of a national climate resilience programme. Independent analyses have cautioned that too little consideration was being paid to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK must "prepare for two degrees of warming" and examine the risks for four degrees. Previous adaptation plans have been described as being "insufficient" by environmental groups.

A national response said: "The climate emergency is at the center of our national priorities, both building resilience and transitioning to a renewable energy leader. It is essential that the UK is resilient for the effects."