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The direst possible consequences of the global heating for the UK have been detailed by experts, encompassing a searing 4C increase in mean temperatures to a 6.5-foot increase in sea levels. Another scenario predicts a plunge of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would severely impact agriculture and power requirements.

Possible Extremes, Not Forecasts

These impacts, a number of which are connected to climate tipping points, are viewed as improbable but possible. The researchers stated that these scenarios filled a gap in risk assessment that had rendered the UK ill-prepared for extreme outcomes.

"The climate extremes we have outlined aren’t predictions, but they are credible," commented the professor who directed the analysis. "The UK has been planning lacking the tools to plan for worst-case scenarios. We've now supplied planners what they need to get ready for environmental results they wish to avoid, but can’t afford to ignore."

A Suite of Extreme Weather Scenarios

A further series of severe models details the projected severity of extreme weather between now and the close of the 2100s. These show that thermometer readings could rocket in particular seasons by up to 6C higher than historical levels, while precipitation could be three times standard measurements.

The probability of the worst-case outcomes occurring cannot be precisely determined due to uncertainty about what measures will be implemented to combat global warming and how the planet's climate will react. This research was likened to security threat evaluations or resilience checks for the banking sector.

Critical Scenario Elements

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could happen if climate action breaks down or if strong feedback loops like the tropical forests becoming a net carbon source emit its vast reserves of carbon. This would cause extreme and prolonged heatwaves and droughts plaguing the UK in summer.
• Ocean Circulation Failure: A key circulation system, the AMOC, is slowing down and showing signs of collapse due to climate change. A full shutdown commencing by 2030 would lead to a drastic cooling in the UK. "Crop production would face immense difficulties and water supplies would be drastically changed," explained the lead researcher.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the Arctic and Antarctic melt abruptly, inundating coastal cities and towns. Unlike the other scenarios, this threat is already understood by coastal engineers.
• Clean Air Warming: Temperatures could also be increased by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from fossil fuel combustion reflect solar radiation from reaching the ground.

Building Resilience Against the Worst

The worst-case scenarios could be used to inform the construction of major projects, including housing developments, nuclear power stations and urban drainage systems. Awareness of these climate risks could also accelerate the drive to reduce fossil fuel emissions.

The research developed the extreme models using a mix of real-world events, digital projections and climate physics. These outcomes omit international cascading effects such as the devastation of food supplies and resource wars.

The research was initiated as part of a national risk assessment framework. Independent analyses have warned that not enough attention was being paid to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK must "become resilient to moderate heating" and examine the threats for four degrees. Past policy documents have been labeled being "inadequate" by environmental groups.

A national response commented: "Global warming is at the core of this government’s agenda, both adapting for the future and establishing itself as a low-carbon economy. It is crucial that the UK is resilient for the effects."