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The most severe projected effects of the climate emergency for the UK have been outlined by experts, encompassing a searing 4C increase in temperatures to a 2-metre surge in sea level. Another scenario predicts a plunge of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would severely impact agriculture and energy needs.

Possible Outcomes, Not Predictions

These impacts, some of which are associated with climate tipping points, are viewed as unlikely but credible. The team said that these models plugged a hole in forecasting that had left the UK unprepared for worst-case results.

"The climate extremes we have detailed aren’t predictions, but they are credible," said the lead researcher who led the study. "The UK has been formulating policy lacking the frameworks to test against extreme possibilities. We've now supplied policymakers what they need to plan for climate outcomes they hope never happen, but can’t afford to ignore."

A Suite of Severe Conditions Scenarios

A further series of worst-case scenarios maps the possible scale of harsh climate between now and the year 2100. These show that temperatures could soar in particular seasons by up to 6C higher than historical levels, while precipitation could be three times normal levels.

The chance of the catastrophic events occurring could not be calculated due to a lack of certainty about what measures will be taken to address global heating and how the Earth's systems will behave. This research was described as similar to security threat evaluations or scenario planning for financial systems.

Critical Outcome Details

• Severe Heating: Worldwide averages exceeding 4C by 2100 could happen if emissions cuts fails or if vicious cycles such as the tropical forests becoming a net carbon source release its huge repository of carbon. This would lead to intense and enduring heatwaves and dry spells affecting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is weakening and showing signs of collapse due to climate change. A complete failure beginning in 2030 would lead to a 6C cooling in the UK. "Agriculture would be severely challenged and freshwater availability would be fundamentally reshaped," noted the lead researcher.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions collapse rapidly, flooding coastal cities and towns. In contrast to the other scenarios, this possibility is already known by coastal engineers.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if airborne particulates is rapidly cleaned up. This unexpected result occurs because aerosol particles from burning coal block sunlight from reaching the ground.

Building Resilience Against the Unthinkable

The severe models could be utilized in planning the building of critical national infrastructure, including new towns, nuclear power stations and urban drainage systems. Understanding these environmental threats could also hasten the push to slash carbon pollution.

The analysis developed the severe projections using a mix of real-world events, digital projections and climate physics. The scenarios omit potential global problems including the global food shortages and increased conflict.

This work was commissioned as part of a national risk assessment framework. Independent analyses have warned that not enough attention was being paid to high-consequence, low-probability risks.

Official experts has said that the UK must "become resilient to moderate heating" and evaluate the risks for four degrees. Past policy documents have been described as being "insufficient" by some observers.

An official statement commented: "Climate change is at the core of the country's focus, both preparing for impacts and transitioning to a clean energy superpower. It is crucial that the UK is ready for the consequences."