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The gravest possible consequences of the climate emergency for the UK have been detailed by experts, ranging from a searing 4C rise in mean temperatures to a two-metre rise in sea levels. A separate possibility envisions a plunge of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would severely impact agriculture and power requirements.

Credible Events, Not Forecasts

These consequences, certain ones are connected to irreversible climate shifts, are considered as improbable but plausible. The scientists explained that these models filled a gap in forecasting that had left the UK not ready for catastrophic possibilities.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are possible," commented the professor who oversaw the analysis. "The UK has been formulating policy lacking the methods to test against catastrophic outcomes. We've now given policymakers what they need to prepare for future conditions they wish to avoid, but dare not dismiss."

A Range of Extreme Weather Scenarios

Another collection of worst-case scenarios sets out the potential extent of extreme weather between now and the close of the 2100s. These suggest that temperatures could soar in certain periods by up to 6C above the norm, while precipitation could be 300% of typical amounts.

The chance of the catastrophic events coming to pass could not be calculated due to a lack of certainty about what action will be taken to combat global heating and how the Earth's systems will behave. This analysis was compared to security threat evaluations or stress tests for economic stability.

Key Outcome Highlights

• Four-Degree Warming: Worldwide averages exceeding 4C by 2100 could happen if climate action collapses or if strong feedback loops such as the Amazon rainforest becoming a net carbon source release its enormous store of carbon. This would cause extreme and prolonged heatwaves and water shortages plaguing the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is losing strength and becoming unstable due to global heating. A complete failure starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and water supplies would be drastically changed," noted Arnell.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the polar regions collapse rapidly, inundating coastal cities and towns. Differing from the other scenarios, this possibility is already known by coastal engineers.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if pollution from industry is sharply cut. This counterintuitive effect occurs because pollution particles from burning coal reflect solar radiation from warming the ground.

Planning for the Extreme

The worst-case scenarios could be used to inform the development of long-term infrastructure, including new towns, nuclear power stations and flood defences. Awareness of these future hazards could also speed the push to cut greenhouse gas emissions.

The study developed the extreme models using a combination of observed and historical experience, climate models and established principles. These outcomes exclude broader worldwide issues like the global food shortages and resource wars.

The research was requested as part of a government’s risk assessment framework. Independent analyses have stated that not enough attention was being given to catastrophic yet improbable risks.

An independent advisory body has said that the UK needs to "adapt to 2C" and assess the risks for severe warming. Earlier government strategies have been described as being "insufficient" by some observers.

A government spokesperson commented: "Global warming is at the center of our national priorities, both preparing for impacts and becoming a renewable energy leader. It is vital that the UK is prepared for the effects."