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The gravest possible consequences of the climate emergency for the UK have been detailed by scientists, including a searing 4C jump in mean temperatures to a two-metre rise in sea levels. An alternative projection envisions a drop of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would severely impact farming and energy needs.

Possible Outcomes, Not Guarantees

These effects, certain ones are linked to critical climate thresholds, are considered as improbable but possible. The researchers explained that these models filled a gap in forecasting that had rendered the UK unprepared for extreme outcomes.

"The climate extremes we have outlined should not be seen as certainties, but they are plausible," said the professor who led the research. "Britain has been making preparations lacking the methods to test against worst-case scenarios. We've now given policymakers what they need to plan for future conditions they hope never happen, but dare not dismiss."

A Spectrum of Harsh Climate Scenarios

A further series of severe models sets out the projected severity of harsh climate between now and the year 2100. These show that thermometer readings could skyrocket in certain periods by up to 6C higher than the norm, while rainfall could be 300% of normal levels.

The likelihood of the worst-case outcomes occurring remains uncertain due to uncertainty about what action will be implemented to address global heating and how the climate system will behave. This approach was compared to security threat evaluations or resilience checks for economic stability.

Major Outcome Highlights

• 4C Temperature Rise: Planetary heating soaring past 4C by 2100 could occur if international cooperation fails or if powerful amplifying effects such as the Amazon basin perishing unleash its huge repository of carbon. This would lead to extreme and prolonged heat domes and droughts affecting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is weakening and losing stability due to global heating. A full shutdown beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and freshwater availability would be fundamentally reshaped," 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 disintegrate quickly, submerging seaside communities. Unlike the other scenarios, this threat is already understood by coastal engineers.
• Aerosol Effect: Global averages 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 scatter sunlight from reaching the ground.

Preparing for the Extreme

These dire projections could be used to inform the construction of long-term infrastructure, for example new towns, power generation facilities and water management networks. Knowledge about these climate risks could also accelerate the transition to slash carbon pollution.

The analysis formulated the severe projections using a mix of real-world events, digital projections and established principles. The possibilities omit potential global problems such as the global food shortages and increased conflict.

The project was requested as part of a national adaptation planning initiative. Independent analyses have warned that insufficient focus was being allocated to catastrophic yet improbable risks.

An independent advisory body has stated that the UK must "become resilient to moderate heating" and assess the threats for severe warming. Previous adaptation plans have been labeled being "very weak" by environmental groups.

An official statement commented: "Global warming is at the center of our national priorities, both preparing for impacts and becoming a clean energy superpower. It is vital that the UK is ready for the effects."