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The gravest possible consequences of the climate emergency for the UK have been detailed by scientists, ranging from a searing 4C increase in temperatures to a 2-metre surge in ocean levels. An alternative projection predicts a decline of 6C in temperature following the failure of key Atlantic Ocean currents, which would severely impact food production and energy needs.

Credible Events, Not Predictions

These consequences, certain ones are linked to climate tipping points, are considered as unlikely but plausible. The scientists stated that these models plugged a hole in planning that had rendered the UK not ready for worst-case results.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are plausible," commented Nigel Arnell who oversaw the analysis. "Britain has been formulating policy lacking the tools to plan for catastrophic outcomes. We've now given policymakers what they need to get ready for environmental results they pray never occur, but must not overlook."

A Spectrum of Harsh Climate Projections

Another collection of dire projections maps the possible scale of severe conditions between now and the year 2100. These indicate that thermometer readings could rocket in certain periods by up to 6C above average, while rainfall could be 300% of normal levels.

The likelihood of the catastrophic events occurring could not be calculated due to uncertainty about what steps will be taken to tackle global warming and how the climate system will behave. This approach was likened to national security risk assessments or stress tests for economic stability.

Critical Possibility Details

• Four-Degree Warming: Planetary heating exceeding 4C by 2100 could happen if climate action collapses or if vicious cycles including the Amazon basin perishing release its huge repository of carbon. This would lead to severe and lengthy heat domes and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is losing strength and showing signs of collapse due to climate change. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Crop production would be severely challenged and water supplies would be completely altered," noted Arnell.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in the polar regions melt abruptly, flooding low-lying areas. Unlike the other scenarios, this possibility is already recognized by infrastructure experts.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if pollution from industry is sharply cut. This paradoxical outcome occurs because pollution particles from fossil fuel combustion scatter sunlight from reaching the ground.

Building Resilience Against the Worst

The severe models could be applied to guide the building of long-term infrastructure, for example expanded cities, nuclear power stations and flood defences. Understanding these future hazards could also speed the push to cut fossil fuel emissions.

The research formulated the worst-case scenarios using a blend of real-world events, computer simulations and scientific theory. The possibilities omit potential global problems like the devastation of food supplies and increased conflict.

The research was initiated as part of a national risk assessment framework. Independent analyses have warned that too little consideration was being allocated to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK needs to "adapt to 2C" and examine the risks for 4C. Previous adaptation plans have been labeled being "very weak" by environmental groups.

A government spokesperson said: "Climate change is at the heart of our national priorities, both adapting for the future and transitioning to a renewable energy leader. It is crucial that the UK is resilient for the consequences."