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The direst projected effects of the climate crisis for the UK have been outlined by scientists, ranging from a searing 4C rise in mean temperatures to a two-metre surge in sea levels. An alternative projection foresees a drop of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would massively disrupt food production and power requirements.

Plausible Outcomes, Not Guarantees

These impacts, some of which are associated with climate tipping points, are viewed as improbable but plausible. The scientists explained that these projections filled a gap in risk assessment that had left the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are credible," stated the lead researcher who directed the study. "The UK has been making preparations lacking the tools to plan for catastrophic outcomes. We've now provided decision-makers what they need to plan for future conditions they pray never occur, but dare not dismiss."

A Spectrum of Severe Conditions Projections

A second set of dire projections details the potential extent of severe conditions between now and the year 2100. These indicate that thermometer readings could rocket in some months by up to 6C higher than average, while rainfall could be 300% of standard measurements.

The likelihood of the worst-case outcomes occurring remains uncertain due to uncertainty about what measures will be implemented to tackle climate change and how the climate system will respond. This approach was likened to defence planning or stress tests for the banking sector.

Major Scenario Elements

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could transpire if emissions cuts fails or if strong feedback loops including the Amazon basin becoming a net carbon source release its vast reserves of carbon. This would result in intense and enduring heat domes and dry spells affecting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is weakening and losing stability due to ocean warming. A collapse commencing by 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would be severely challenged and water resources would be drastically changed," said the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the polar regions disintegrate quickly, inundating seaside communities. Differing from the other scenarios, this threat is already recognized by infrastructure experts.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because aerosol particles from fossil fuel combustion reflect solar radiation from warming the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be applied to guide the development of critical national infrastructure, including expanded cities, nuclear power stations and urban drainage systems. Awareness of these environmental threats could also hasten the push to cut fossil fuel emissions.

The study created the worst-case scenarios using a combination of past data and records, climate models and scientific theory. The scenarios omit international cascading effects such as the devastation of food supplies and increased conflict.

The research was initiated as part of a national risk assessment framework. Previous assessments have stated that not enough attention was being paid to high-consequence, low-probability risks.

Official experts has recommended that the UK must "prepare for two degrees of warming" and examine the threats for 4C. Past policy documents have been labeled being "inadequate" by certain experts.

A national response noted: "The climate emergency is at the core of this government’s agenda, both preparing for impacts and becoming a clean energy superpower. It is vital that the UK is resilient for the effects."