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The gravest projected effects of the climate emergency for the UK have been detailed by scientists, encompassing a scorching 4C jump in temperatures to a two-metre surge in sea level. An alternative projection foresees a decline of 6C in temperatures following the collapse of crucial Atlantic Ocean currents, which would massively disrupt agriculture and power requirements.

Plausible Outcomes, Not Predictions

These consequences, certain ones are linked to irreversible climate shifts, are seen as improbable but possible. The researchers said that these projections filled a gap in planning that had rendered the UK not ready for catastrophic possibilities.

"The climate extremes we have outlined aren’t predictions, but they are possible," said Nigel Arnell who led the analysis. "The nation has been planning without the frameworks to plan for catastrophic outcomes. We've now given decision-makers what they need to plan for environmental results they hope never happen, but must not overlook."

A Suite of Extreme Weather Scenarios

A further series of worst-case scenarios sets out the potential extent of extreme weather between now and the close of the 2100s. These indicate that thermometer readings could soar in certain periods by up to 6C above the norm, while precipitation could be triple normal levels.

The chance of the catastrophic events occurring remains uncertain due to a lack of certainty about what action will be implemented to tackle global heating and how the planet's climate will react. This research was compared to security threat evaluations or stress tests for financial systems.

Major Outcome Details

• Severe Heating: Planetary heating soaring past 4C by 2100 could occur if international cooperation collapses or if powerful amplifying effects such as the Amazon basin becoming a net carbon source unleash its vast reserves of carbon. This would cause intense and enduring heat domes and droughts hitting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is weakening and becoming unstable due to ocean warming. A full shutdown beginning in 2030 would lead to a 6C cooling in the UK. "Farming 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 happen if polar ice in Greenland and Antarctica disintegrate quickly, flooding seaside communities. Differing from the other scenarios, this possibility is already understood by infrastructure experts.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if industrial aerosols is drastically reduced. This unexpected result occurs because aerosol particles from burning coal scatter sunlight from reaching the ground.

Planning for the Extreme

The severe models could be applied to guide the construction of major projects, such as expanded cities, nuclear power stations and urban drainage systems. Knowledge about these climate risks could also hasten the transition to cut greenhouse gas emissions.

The study developed the severe projections using a blend of observed and historical experience, digital projections and established principles. The scenarios do not take into account broader worldwide issues including the agricultural collapse and increased conflict.

This work was initiated as part of a official risk assessment framework. Previous assessments have stated that not enough attention was being paid to high-consequence, low-probability risks.

An independent advisory body has said that the UK must "become resilient to moderate heating" and examine the dangers for severe warming. Previous adaptation plans have been described as being "very weak" by some observers.

An official statement noted: "Global warming is at the center of the country's focus, both building resilience and establishing itself as a renewable energy leader. It is crucial that the UK is prepared for the consequences."