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The direst projected effects of the climate crisis for the UK have been mapped by researchers, ranging from a blistering 4C rise in mean temperatures to a 2-metre rise in sea levels. Another scenario foresees a decline of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would massively disrupt food production and energy demand.

Credible Events, Not Guarantees

These impacts, a number of which are linked to critical climate thresholds, are considered as unlikely but possible. The scientists stated that these projections addressed a shortfall in forecasting that had rendered the UK unprepared for worst-case results.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are possible," said Nigel Arnell who led the research. "The nation has been planning lacking the tools to test against catastrophic outcomes. We've now given decision-makers what they need to prepare for future conditions they pray never occur, but can’t afford to ignore."

A Range of Harsh Climate Possibilities

A further series of worst-case scenarios maps the projected severity of extreme weather between now and the close of the 2100s. These indicate that thermometer readings could soar in some months by up to 6C above the norm, while precipitation could be three times typical amounts.

The likelihood of the extreme scenarios occurring cannot be precisely determined due to a lack of certainty about what action will be taken to combat climate change and how the planet's climate will react. This research was described as similar to security threat evaluations or stress tests for financial systems.

Major Outcome Elements

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could transpire if international cooperation breaks down or if powerful amplifying effects including the Amazon basin becoming a net carbon source release its vast reserves of carbon. This would cause intense and enduring heatwaves and water shortages hitting the UK in summer.
• Ocean Circulation Failure: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is losing strength and showing signs of collapse due to ocean warming. A collapse commencing by 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and water supplies would be drastically changed," noted the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the polar regions disintegrate quickly, flooding low-lying areas. In contrast to the other scenarios, this risk is already understood by infrastructure experts.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because pollution particles from burning coal scatter solar radiation from warming the ground.

Preparing for the Unthinkable

These dire projections could be used to inform the building of long-term infrastructure, such as new towns, nuclear power stations and urban drainage systems. Awareness of these environmental threats could also speed the push to slash greenhouse gas emissions.

The analysis created the severe projections using a mix of past data and records, climate models and scientific theory. The scenarios exclude broader worldwide issues like the devastation of food supplies and geopolitical instability.

The project was commissioned as part of a government’s risk assessment framework. Previous assessments have stated that insufficient focus was being paid to low‐likelihood but high‐impact risks.

The government's climate advisors has recommended that the UK must "become resilient to moderate heating" and evaluate the threats for four degrees. Earlier government strategies have been criticised as being "insufficient" by some observers.

An official statement said: "Global warming is at the center of our national priorities, both building resilience and becoming a clean energy superpower. It is essential that the UK is prepared for the consequences."