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The gravest projected effects of the climate crisis for the UK have been detailed by researchers, including a blistering 4C jump in mean temperatures to a 6.5-foot surge in sea level. Another scenario foresees a drop of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would massively disrupt agriculture and energy needs.

Possible Events, Not Predictions

These impacts, certain ones are linked to climate tipping points, are considered as improbable but credible. The researchers stated that these scenarios plugged a hole in planning that had left the UK ill-prepared for worst-case results.

"The severe weather events we have detailed should not be seen as certainties, but they are possible," commented the professor who oversaw the study. "The UK has been making preparations without the frameworks to test against extreme possibilities. We've now given planners what they need to get ready for future conditions they wish to avoid, but must not overlook."

A Spectrum of Harsh Climate Projections

A second set of dire projections sets out the projected severity of harsh climate between now and the end of the century. These indicate that thermometer readings could rocket in particular seasons by up to 6C higher than historical levels, while rainfall could be triple typical amounts.

The likelihood of the worst-case outcomes occurring remains uncertain due to a lack of certainty about what steps will be taken to address global warming and how the planet's climate will respond. This analysis was likened to national security risk assessments or scenario planning for the banking sector.

Critical Outcome Elements

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could transpire if climate action fails or if strong feedback loops including the Amazon rainforest dying unleash its vast reserves of carbon. This would cause intense and enduring heat domes and droughts plaguing the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is losing strength and showing signs of collapse due to global heating. A complete failure beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and water supplies would be drastically changed," said Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the polar regions disintegrate quickly, inundating seaside communities. Differing from the other scenarios, this threat is already understood by infrastructure experts.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because aerosol particles from industrial activity reflect sunlight from warming the ground.

Preparing for the Worst

The worst-case scenarios could be used to inform the building of major projects, such as housing developments, power generation facilities and urban drainage systems. Knowledge about these future hazards could also hasten the drive to slash fossil fuel emissions.

The analysis created the worst-case scenarios using a blend of real-world events, climate models and established principles. The possibilities do not take into account broader worldwide issues such as the global food shortages and resource wars.

The research was commissioned as part of a government’s risk assessment framework. Independent analyses have warned that insufficient focus was being allocated to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK needs to "adapt to 2C" and assess the risks for four degrees. Earlier government strategies have been described as being "insufficient" by environmental groups.

An official statement noted: "Global warming is at the center of the country's focus, both adapting for the future and transitioning to a renewable energy leader. It is vital that the UK is prepared for the consequences."