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The gravest projected effects of the climate crisis for the UK have been outlined by researchers, including a searing 4C increase in mean temperatures to a 2-metre increase in sea levels. A separate possibility predicts a plunge of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would severely impact farming and energy demand.

Credible Events, Not Predictions

These impacts, some of which are connected to irreversible climate shifts, are viewed as low probability but credible. The researchers stated that these models addressed a shortfall in planning that had left the UK unprepared for worst-case results.

"The worst-case scenarios we have outlined aren’t predictions, but they are plausible," commented Nigel Arnell who directed the study. "The nation has been making preparations lacking the methods to test against worst-case scenarios. We've now given decision-makers what they need to get ready for climate outcomes they wish to avoid, but dare not dismiss."

A Range of Extreme Weather Possibilities

Another collection of dire projections sets out the projected severity of harsh climate between now and the year 2100. These show that thermometer readings could rocket in some months by up to 6C above historical levels, while rainfall could be triple normal levels.

The chance of the extreme scenarios coming to pass cannot be precisely determined due to unknown factors about what steps will be taken to address global heating and how the Earth's systems will react. This research was compared to national security risk assessments or scenario planning for the banking sector.

Major Possibility Elements

• 4C Temperature Rise: Planetary heating rising well above 4C by 2100 could occur if emissions cuts fails or if strong feedback loops such as the Amazon basin becoming a net carbon source unleash its enormous store of carbon. This would lead to severe and lengthy heat domes and droughts hitting the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is weakening and becoming unstable due to global heating. A complete failure starting around 2030 would lead to a 6C cooling in the UK. "Agriculture would be severely challenged and water supplies would be completely altered," noted Arnell.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in Greenland and Antarctica disintegrate quickly, flooding low-lying areas. Unlike the other scenarios, this threat is already understood by infrastructure experts.
• Clean Air Warming: Temperatures could also be increased by about 0.75C if airborne particulates is sharply cut. This paradoxical outcome occurs because aerosol particles from fossil fuel combustion block solar radiation from warming the ground.

Preparing for the Worst

The worst-case scenarios could be applied to guide the building of long-term infrastructure, for example new towns, nuclear power stations and water management networks. Awareness of these future hazards could also speed the transition to cut fossil fuel emissions.

The analysis formulated the extreme models using a mix of real-world events, digital projections and established principles. These outcomes do not take into account broader worldwide issues like the devastation of food supplies and geopolitical instability.

The research was commissioned as part of a government’s adaptation planning initiative. Previous assessments have warned that too little consideration was being paid to low‐likelihood but high‐impact risks.

An independent advisory body has recommended that the UK needs to "adapt to 2C" and examine the risks for four degrees. Previous adaptation plans have been described as being "insufficient" by environmental groups.

A national response noted: "Global warming is at the heart of our national priorities, both building resilience and becoming a clean energy superpower. It is essential that the UK is prepared for the effects."