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The most severe potential impacts of the global heating for the UK have been detailed by experts, encompassing a searing 4C jump in average temperatures to a 2-metre rise in sea level. Another scenario foresees a drop of 6C in temperature following the collapse of key Atlantic Ocean currents, which would massively disrupt food production and energy needs.

Credible Extremes, Not Guarantees

These consequences, certain ones are linked to climate tipping points, are viewed as low probability but credible. The researchers said that these scenarios plugged a hole in forecasting that had rendered the UK ill-prepared for extreme outcomes.

"The worst-case scenarios we have mapped aren’t predictions, but they are possible," commented the lead researcher who led the research. "The nation has been formulating policy lacking the tools to plan for catastrophic outcomes. We've now provided policymakers what they need to plan for environmental results they wish to avoid, but can’t afford to ignore."

A Range of Severe Conditions Possibilities

A further series of worst-case scenarios details the possible scale of severe conditions between now and the end of the century. These show that thermometer readings could soar in particular seasons by up to 6C higher than historical levels, while precipitation could be 300% of typical amounts.

The chance of the worst-case outcomes coming to pass could not be calculated due to a lack of certainty about what steps will be taken to address global warming and how the climate system will react. This analysis was compared to security threat evaluations or scenario planning for the banking sector.

Major Possibility Details

• 4C Temperature Rise: Global temperatures rising well above 4C by 2100 could happen if emissions cuts collapses or if strong feedback loops including the Amazon rainforest becoming a net carbon source release its vast reserves of carbon. This would lead to extreme and prolonged heatwaves and dry spells hitting the UK in summer.
• AMOC Shutdown: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is slowing down and becoming unstable due to ocean warming. A complete failure starting around 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would face immense difficulties and water supplies would be drastically changed," noted the lead researcher.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in Greenland and Antarctica melt abruptly, submerging low-lying areas. In contrast to the other scenarios, this possibility is already understood by planners.
• Aerosol Effect: Global averages could also be increased by about 0.75C if industrial aerosols is drastically reduced. This paradoxical outcome occurs because tiny specks from fossil fuel combustion reflect solar radiation from warming the ground.

Planning for the Worst

The severe models could be utilized in planning the development of critical national infrastructure, including expanded cities, power generation facilities and flood defences. Knowledge about these environmental threats could also speed the transition to cut greenhouse gas emissions.

The study developed the worst-case scenarios using a blend of real-world events, computer simulations and scientific theory. The possibilities omit potential global problems such as the global food shortages and increased conflict.

The research was initiated as part of a government’s adaptation planning initiative. Previous assessments have warned that too little consideration was being paid to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK must "prepare for two degrees of warming" and examine the dangers for severe warming. Past policy documents have been criticised as being "very weak" by environmental groups.

A government spokesperson said: "Global warming is at the heart of this government’s agenda, both adapting for the future and becoming a clean energy superpower. It is essential that the UK is prepared for the effects."