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The direst possible consequences of the climate crisis for the UK have been outlined by scientists, encompassing a scorching 4C rise in average temperatures to a 2-metre increase in ocean levels. A separate possibility predicts a decline of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would severely impact food production and energy demand.

Credible Outcomes, Not Predictions

These effects, some of which are connected to climate tipping points, are seen as unlikely but plausible. The researchers explained that these models addressed a shortfall in risk assessment that had left the UK unprepared for extreme outcomes.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are plausible," said the professor who oversaw the analysis. "Britain has been making preparations without the tools to plan for catastrophic outcomes. We've now provided policymakers what they need to get ready for climate outcomes they hope never happen, but can’t afford to ignore."

A Range of Severe Conditions Possibilities

A second set of worst-case scenarios details the projected severity of extreme weather between now and the close of the 2100s. These indicate that temperatures could rocket in some months by up to 6C higher than historical levels, while precipitation could be three times normal levels.

The likelihood of the catastrophic events coming to pass could not be calculated due to a lack of certainty about what measures will be enacted to combat global warming and how the climate system will respond. This research was likened to security threat evaluations or stress tests for economic stability.

Major Scenario Elements

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could occur if emissions cuts collapses or if powerful amplifying effects like the Amazon rainforest dying unleash its vast reserves of carbon. This would result in severe and lengthy heat domes and water shortages affecting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and becoming unstable due to global heating. A collapse beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would struggle enormously and water supplies would be completely altered," noted Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica collapse rapidly, inundating coastal cities and towns. Differing from the other scenarios, this risk is already understood by coastal engineers.
• Aerosol Effect: Global averages could also be driven up by about 0.75C if pollution from industry is sharply cut. This counterintuitive effect occurs because tiny specks from fossil fuel combustion reflect solar radiation from reaching the ground.

Planning for the Unthinkable

The severe models could be utilized in planning the development of major projects, such as new towns, power generation facilities and water management networks. Understanding these climate risks could also accelerate the drive to cut carbon pollution.

The analysis developed the worst-case scenarios using a blend of real-world events, computer simulations and established principles. The scenarios omit broader worldwide issues such as the devastation of food supplies and geopolitical instability.

The project was commissioned as part of a national risk assessment framework. Previous assessments have cautioned that insufficient focus was being paid to high-consequence, low-probability risks.

An independent advisory body has recommended that the UK needs to "become resilient to moderate heating" and assess the risks for four degrees. Previous adaptation plans have been labeled being "insufficient" by certain experts.

A government spokesperson noted: "The climate emergency is at the center of this government’s agenda, both preparing for impacts and becoming a renewable energy leader. It is crucial that the UK is resilient for the effects."