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The most severe possible consequences of the climate crisis for the UK have been mapped by experts, ranging from a scorching 4C rise in average temperatures to a 2-metre increase in sea level. A separate possibility predicts a drop of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would massively disrupt agriculture and power requirements.

Credible Events, Not Guarantees

These impacts, some of which are linked to irreversible climate shifts, are seen as unlikely but plausible. The team said that these projections filled a gap in planning that had left the UK ill-prepared for worst-case results.

"The worst-case scenarios we have detailed aren’t predictions, but they are credible," said the professor who directed the analysis. "The nation has been planning lacking the tools to plan for extreme possibilities. We've now given planners what they need to plan for environmental results they pray never occur, but can’t afford to ignore."

A Spectrum of Extreme Weather Projections

Another collection of worst-case scenarios sets out the possible scale of extreme weather between now and the end of the century. These show that thermometer readings could soar in particular seasons by up to 6C higher than average, while rainfall could be three times standard measurements.

The probability of the catastrophic events happening could not be calculated due to unknown factors about what measures will be enacted to combat global warming and how the Earth's systems will respond. This analysis was described as similar to national security risk assessments or resilience checks for the banking sector.

Major Possibility Elements

• Severe Heating: Worldwide averages soaring past 4C by 2100 could happen if international cooperation fails or if vicious cycles including the tropical forests dying unleash its vast reserves of carbon. This would lead to extreme and prolonged heatwaves and dry spells hitting the UK in summer.
• AMOC Shutdown: A key circulation system, the North Atlantic current, is losing strength and showing signs of collapse due to global heating. A collapse commencing by 2030 would lead to a 6C cooling in the UK. "Agriculture would face immense difficulties and water supplies would be fundamentally reshaped," said the lead researcher.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the polar regions collapse rapidly, inundating coastal cities and towns. In contrast to the other scenarios, this possibility is already understood by planners.
• Aerosol Effect: Temperatures could also be pushed higher by about 0.75C if industrial aerosols is drastically reduced. This unexpected result occurs because pollution particles from industrial activity block solar radiation from reaching the ground.

Preparing for the Unthinkable

The worst-case scenarios could be utilized in planning the construction of critical national infrastructure, for example expanded cities, nuclear power stations and water management networks. Understanding these future hazards could also hasten the push to reduce greenhouse gas emissions.

The analysis formulated the worst-case scenarios using a blend of past data and records, computer simulations and established principles. The possibilities exclude broader worldwide issues like the agricultural collapse and geopolitical instability.

The research was requested as part of a government’s adaptation planning initiative. Earlier reports have warned that too little consideration was being given to low‐likelihood but high‐impact risks.

The government's climate advisors has stated that the UK needs to "prepare for two degrees of warming" and examine the dangers for four degrees. Previous adaptation plans have been labeled being "insufficient" by certain experts.

An official statement said: "Global warming is at the heart of this government’s agenda, both adapting for the future and transitioning to a renewable energy leader. It is essential that the UK is prepared for the effects."