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The direst potential impacts of the climate emergency for the UK have been mapped by scientists, ranging from a searing 4C increase in mean temperatures to a 2-metre rise in sea level. An alternative projection envisions a decline of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would massively disrupt food production and power requirements.

Possible Outcomes, Not Predictions

These consequences, some of which are linked to critical climate thresholds, are seen as improbable but possible. The researchers stated that these scenarios addressed a shortfall in planning that had rendered the UK not ready for worst-case results.

"The worst-case scenarios we have mapped aren’t predictions, but they are possible," said the professor who oversaw the analysis. "Britain has been making preparations lacking the tools to test against catastrophic outcomes. We've now given policymakers what they need to prepare for climate outcomes they pray never occur, but can’t afford to ignore."

A Range of Severe Conditions Possibilities

A second set of worst-case scenarios maps the projected severity of extreme weather between now and the end of the century. These show that thermometer readings could rocket in certain periods by up to 6C higher than average, while precipitation could be triple standard measurements.

The likelihood of the catastrophic events occurring remains uncertain due to uncertainty about what measures will be implemented to tackle global heating and how the planet's climate will react. This approach was compared to security threat evaluations or resilience checks for economic stability.

Major Outcome Elements

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could transpire if climate action breaks down or if powerful amplifying effects like the tropical forests becoming a net carbon source release its huge repository of carbon. This would result in extreme and prolonged heat domes and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the AMOC, is slowing down and losing stability due to global heating. A full shutdown starting around 2030 would lead to a drastic cooling in the UK. "Crop production would struggle enormously and freshwater availability would be completely altered," explained Arnell.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the polar regions collapse rapidly, inundating low-lying areas. In contrast to the other scenarios, this risk is already known by planners.
• Clean Air Warming: Global averages could also be increased by about 0.75C if industrial aerosols is sharply cut. This unexpected result occurs because tiny specks from fossil fuel combustion block solar radiation from reaching the ground.

Preparing for the Extreme

The worst-case scenarios could be utilized in planning the building of critical national infrastructure, for example housing developments, power generation facilities and flood defences. Understanding these climate risks could also speed the drive to slash fossil fuel emissions.

The research developed the severe projections using a mix of observed and historical experience, digital projections and scientific theory. These outcomes do not take into account broader worldwide issues like the global food shortages and increased conflict.

This work was initiated as part of a government’s risk assessment framework. Independent analyses have stated that too little consideration was being given to low‐likelihood but high‐impact risks.

Official experts has recommended that the UK must "adapt to 2C" and assess the risks for severe warming. Past policy documents have been described as being "very weak" by certain experts.

A national response commented: "Global warming is at the heart of our national priorities, both adapting for the future and establishing itself as a renewable energy leader. It is essential that the UK is prepared for the consequences."