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The gravest projected effects of the global heating for the UK have been detailed by experts, ranging from a blistering 4C rise in temperatures to a two-metre increase in ocean levels. An alternative projection envisions a plunge of 6C in temperature following the collapse of key Atlantic Ocean currents, which would profoundly upset farming and energy needs.

Plausible Extremes, Not Predictions

These effects, some of which are connected to climate tipping points, are seen as low probability but credible. The researchers explained that these scenarios plugged a hole in planning that had rendered the UK not ready for catastrophic possibilities.

"The worst-case scenarios we have detailed aren’t predictions, but they are possible," stated Nigel Arnell who oversaw the study. "The nation has been making preparations lacking the frameworks to assess catastrophic outcomes. We've now provided policymakers what they need to prepare for future conditions they pray never occur, but can’t afford to ignore."

A Suite of Severe Conditions Possibilities

A second set of worst-case scenarios sets out the possible scale of severe conditions between now and the year 2100. These indicate that thermometer readings could skyrocket in certain periods by up to 6C higher than the norm, while precipitation could be triple normal levels.

The chance of the extreme scenarios happening could not be calculated due to a lack of certainty about what steps will be enacted to combat global warming and how the planet's climate will react. This approach was compared to security threat evaluations or stress tests for the banking sector.

Major Possibility Elements

• Four-Degree Warming: Worldwide averages soaring past 4C by 2100 could happen if international cooperation breaks down or if vicious cycles such as the Amazon rainforest perishing release its huge repository of carbon. This would cause severe and lengthy heat domes and water shortages plaguing the UK in summer.
• Atlantic Current Collapse: A critical sea current, the North Atlantic current, is losing strength and becoming unstable due to ocean warming. A full shutdown commencing by 2030 would lead to a drastic cooling in the UK. "Farming would struggle enormously and water supplies would be fundamentally reshaped," explained the professor.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the polar regions disintegrate quickly, inundating low-lying areas. In contrast to the other scenarios, this threat is already recognized by coastal engineers.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if airborne particulates is rapidly cleaned up. This counterintuitive effect occurs because pollution particles from industrial activity block solar radiation from reaching the ground.

Building Resilience Against the Worst

The worst-case scenarios could be used to inform the development of critical national infrastructure, for example housing developments, nuclear power stations and flood defences. Awareness of these environmental threats could also speed the transition to cut greenhouse gas emissions.

The study created the extreme models using a mix of past data and records, computer simulations and established principles. The scenarios do not take into account potential global problems like the global food shortages and increased conflict.

This work was initiated as part of a official climate resilience programme. Independent analyses have cautioned that insufficient focus was being given to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK needs to "prepare for two degrees of warming" and evaluate the threats for 4C. Earlier government strategies have been criticised as being "insufficient" by certain experts.

A national response noted: "The climate emergency is at the core of our national priorities, both building resilience and becoming a renewable energy leader. It is crucial that the UK is ready for the effects."