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The direst potential impacts of the global heating for the UK have been outlined by scientists, ranging from a blistering 4C increase in average temperatures to a 6.5-foot increase in sea level. Another scenario foresees a drop of 6C in temperatures following the failure of critical Atlantic Ocean currents, which would severely impact farming and power requirements.

Possible Outcomes, Not Predictions

These effects, a number of which are connected to climate tipping points, are viewed as improbable but possible. The scientists stated that these models addressed a shortfall in risk assessment that had left the UK ill-prepared for worst-case results.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are plausible," stated the professor who directed the analysis. "The nation has been planning in the absence of the tools to plan for extreme possibilities. We've now supplied policymakers what they need to plan for climate outcomes they wish to avoid, but must not overlook."

A Suite of Extreme Weather Scenarios

A second set of severe models sets out the projected severity of extreme weather between now and the end of the century. These indicate that temperatures could skyrocket in some months by up to 6C above average, while rainfall could be three times standard measurements.

The probability of the extreme scenarios occurring cannot be precisely determined due to uncertainty about what measures will be implemented to tackle global heating and how the planet's climate will respond. This research was likened to national security risk assessments or resilience checks for economic stability.

Critical Scenario Highlights

• Four-Degree Warming: Worldwide averages exceeding 4C by 2100 could occur if climate action breaks down or if powerful amplifying effects like the Amazon rainforest becoming a net carbon source unleash its enormous store of carbon. This would result in severe and lengthy heatwaves and dry spells plaguing the UK in summer.
• AMOC Shutdown: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is slowing down and showing signs of collapse due to climate change. A collapse beginning in 2030 would lead to a drastic cooling in the UK. "Farming would struggle enormously and water resources would be drastically changed," noted the lead researcher.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the polar regions collapse rapidly, inundating seaside communities. Differing from the other scenarios, this threat is already recognized by coastal engineers.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because tiny specks from industrial activity block solar radiation from warming the ground.

Planning for the Worst

The severe models could be utilized in planning the construction of major projects, for example expanded cities, power generation facilities and water management networks. Understanding these climate risks could also hasten the drive to slash greenhouse gas emissions.

The study developed the severe projections using a mix of past data and records, climate models and established principles. The scenarios exclude broader worldwide issues including the devastation of food supplies and increased conflict.

The project was initiated as part of a national climate resilience programme. Earlier reports have stated that insufficient focus was being given to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "become resilient to moderate heating" and evaluate the dangers for four degrees. Past policy documents have been described as being "inadequate" by some observers.

An official statement noted: "The climate emergency is at the center of the country's focus, both preparing for impacts and becoming a renewable energy leader. It is crucial that the UK is ready for the consequences."