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The gravest possible consequences of the climate crisis for the UK have been mapped by experts, ranging from a searing 4C jump in mean temperatures to a 2-metre increase in ocean levels. Another scenario foresees a decline of 6C in temperature following the collapse of key Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Credible Outcomes, Not Predictions

These consequences, certain ones are associated with critical climate thresholds, are considered as low probability but credible. The researchers explained that these projections addressed a shortfall in planning that had left the UK not ready for extreme outcomes.

"The severe weather events we have outlined should not be seen as certainties, but they are possible," said Nigel Arnell who directed the analysis. "Britain has been formulating policy lacking the tools to test against worst-case scenarios. We've now given decision-makers what they need to plan for climate outcomes they wish to avoid, but can’t afford to ignore."

A Spectrum of Severe Conditions Projections

Another collection of dire projections maps the possible scale of harsh climate between now and the year 2100. These show that temperatures could rocket in particular seasons by up to 6C higher than historical levels, while precipitation could be 300% of typical amounts.

The probability of the worst-case outcomes coming to pass remains uncertain due to unknown factors about what steps will be taken to tackle climate change and how the planet's climate will behave. This approach was described as similar to national security risk assessments or stress tests for financial systems.

Critical Outcome Details

• Four-Degree Warming: Global temperatures soaring past 4C by 2100 could happen if climate action fails or if powerful amplifying effects like the tropical forests perishing emit its enormous store of carbon. This would cause intense and enduring heatwaves and water shortages plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is slowing down and showing signs of collapse due to ocean warming. A full shutdown commencing by 2030 would lead to a drastic cooling in the UK. "Agriculture would struggle enormously and water resources would be completely altered," explained the professor.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the Arctic and Antarctic melt abruptly, submerging low-lying areas. In contrast to the other scenarios, this risk is already recognized by infrastructure experts.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if airborne particulates is sharply cut. This paradoxical outcome occurs because tiny specks from burning coal reflect sunlight from warming the ground.

Building Resilience Against the Unthinkable

The severe models could be utilized in planning the development of long-term infrastructure, including expanded cities, power generation facilities and flood defences. Knowledge about these environmental threats could also hasten the drive to reduce carbon pollution.

The analysis developed the severe projections using a combination of observed and historical experience, climate models and climate physics. The possibilities exclude broader worldwide issues including the global food shortages and increased conflict.

The research was initiated as part of a government’s climate resilience programme. Earlier reports have stated that not enough attention was being paid to high-consequence, low-probability risks.

The government's climate advisors has stated that the UK must "adapt to 2C" and evaluate the threats for 4C. Past policy documents have been labeled being "insufficient" by certain experts.

A national response noted: "The climate emergency is at the heart of this government’s agenda, both building resilience and transitioning to a low-carbon economy. It is essential that the UK is resilient for the impacts."