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The direst possible consequences of the climate emergency for the UK have been detailed by scientists, ranging from a searing 4C rise in average temperatures to a two-metre surge in sea level. Another scenario foresees a plunge of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would severely impact agriculture and power requirements.

Plausible Events, Not Guarantees

These impacts, certain ones are associated with climate tipping points, are viewed as low probability but credible. The researchers said that these scenarios plugged a hole in risk assessment that had rendered the UK ill-prepared for worst-case results.

"The severe weather events we have detailed are not forecasts, but they are credible," stated the lead researcher who oversaw the study. "Britain has been planning in the absence of the frameworks to assess worst-case scenarios. We've now provided policymakers what they need to prepare for future conditions they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Scenarios

Another collection of severe models details the projected severity of extreme weather between now and the end of the century. These show that temperatures could skyrocket in particular seasons by up to 6C above historical levels, while rainfall could be 300% of typical amounts.

The chance of the worst-case outcomes coming to pass remains uncertain due to uncertainty about what action will be implemented to tackle climate change and how the Earth's systems will behave. This approach was described as similar to defence planning or stress tests for economic stability.

Key Outcome Elements

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could transpire if climate action fails or if powerful amplifying effects including the Amazon rainforest dying release its vast reserves of carbon. This would lead to severe and lengthy heatwaves and water shortages plaguing the UK in summer.
• AMOC Shutdown: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is slowing down and becoming unstable due to ocean warming. A complete failure commencing by 2030 would lead to a 6C cooling in the UK. "Farming would struggle enormously and water supplies would be drastically changed," said the professor.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica melt abruptly, inundating seaside communities. In contrast to the other scenarios, this risk is already understood by planners.
• Clean Air Warming: Global averages could also be increased by about 0.75C if airborne particulates is rapidly cleaned up. This unexpected result occurs because pollution particles from fossil fuel combustion scatter solar radiation from warming the ground.

Preparing for the Unthinkable

These dire projections could be applied to guide the development of long-term infrastructure, such as new towns, nuclear power stations and flood defences. Knowledge about these future hazards could also hasten the push to cut greenhouse gas emissions.

The analysis created the severe projections using a combination of past data and records, climate models and climate physics. These outcomes exclude broader worldwide issues such as the devastation of food supplies and geopolitical instability.

The research was commissioned as part of a official risk assessment framework. Earlier reports have stated that too little consideration was being allocated to low‐likelihood but high‐impact risks.

An independent advisory body has recommended that the UK needs to "prepare for two degrees of warming" and assess the dangers for severe warming. Past policy documents have been described as being "inadequate" by some observers.

An official statement said: "Global warming is at the center of our national priorities, both building resilience and becoming a low-carbon economy. It is essential that the UK is ready for the effects."