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The most severe possible consequences of the climate crisis for the UK have been outlined by scientists, ranging from a blistering 4C jump in average temperatures to a 2-metre rise in sea levels. Another scenario envisions a decline of 6C in temperature following the collapse of crucial Atlantic Ocean currents, which would massively disrupt food production and energy demand.

Plausible Outcomes, Not Forecasts

These impacts, some of which are connected to critical climate thresholds, are seen as improbable but possible. The team explained that these projections filled a gap in forecasting that had left the UK not ready for worst-case results.

"The climate extremes we have mapped aren’t predictions, but they are credible," stated the professor who oversaw the research. "The nation has been planning lacking the tools to test against worst-case scenarios. We've now given policymakers what they need to get ready for environmental results they wish to avoid, but can’t afford to ignore."

A Suite of Harsh Climate Scenarios

A further series of severe models details the potential extent of severe conditions between now and the year 2100. These indicate that temperatures could soar in certain periods by up to 6C above average, while rainfall could be three times typical amounts.

The probability of the catastrophic events occurring remains uncertain due to unknown factors about what action will be enacted to tackle climate change and how the climate system will respond. This research was compared to defence planning or resilience checks for economic stability.

Major Outcome Highlights

• Four-Degree Warming: Worldwide averages exceeding 4C by 2100 could transpire if international cooperation breaks down or if powerful amplifying effects like the Amazon rainforest dying release its enormous store of carbon. This would result in severe and lengthy heatwaves and dry spells affecting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is losing strength and becoming unstable due to climate change. A complete failure starting around 2030 would lead to a drastic cooling in the UK. "Farming would face immense difficulties and freshwater availability would be fundamentally reshaped," said Arnell.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the Arctic and Antarctic collapse rapidly, submerging low-lying areas. In contrast to the other scenarios, this risk is already recognized by planners.
• Aerosol Effect: Global averages could also be increased by about 0.75C if airborne particulates is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from burning coal reflect solar radiation from reaching the ground.

Preparing for the Worst

The severe models could be utilized in planning the building of long-term infrastructure, including expanded cities, nuclear power stations and flood defences. Knowledge about these climate risks could also speed the push to slash fossil fuel emissions.

The study created the severe projections using a combination of real-world events, climate models and established principles. The scenarios do not take into account potential global problems such as the devastation of food supplies and geopolitical instability.

The research was requested as part of a official climate resilience programme. Earlier reports have cautioned that too little consideration was being given to high-consequence, low-probability risks.

An independent advisory body has said that the UK must "adapt to 2C" and evaluate the threats for 4C. Past policy documents have been labeled being "very weak" by certain experts.

A government spokesperson noted: "The climate emergency is at the center of our national priorities, both preparing for impacts and establishing itself as a renewable energy leader. It is crucial that the UK is prepared for the impacts."