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The gravest possible consequences of the climate crisis for the UK have been outlined by experts, ranging from a blistering 4C jump in mean temperatures to a two-metre increase in sea level. Another scenario envisions a drop of 6C in temperatures following the collapse of crucial Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Extremes, Not Predictions

These consequences, certain ones are linked to climate tipping points, are considered as low probability but possible. The scientists explained that these projections plugged a hole in forecasting that had rendered the UK unprepared for catastrophic possibilities.

"The climate extremes we have mapped are not forecasts, but they are possible," commented Nigel Arnell who directed the analysis. "The UK has been planning in the absence of the methods to assess catastrophic outcomes. We've now supplied planners what they need to get ready for climate outcomes they hope never happen, but dare not dismiss."

A Spectrum of Extreme Weather Projections

Another collection of worst-case scenarios details the possible scale of extreme weather between now and the end of the century. These indicate that thermometer readings could skyrocket in certain periods by up to 6C above average, while precipitation could be triple typical amounts.

The probability of the catastrophic events happening remains uncertain due to a lack of certainty about what measures will be enacted to address global heating and how the Earth's systems will react. This approach was likened to national security risk assessments or resilience checks for financial systems.

Key Scenario Elements

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could occur if emissions cuts fails or if vicious cycles like the Amazon basin dying release its vast reserves of carbon. This would cause severe and lengthy heat domes and water shortages plaguing the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is weakening and showing signs of collapse due to global heating. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Agriculture would face immense difficulties and water supplies would be drastically changed," said the professor.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in Greenland and Antarctica melt abruptly, submerging coastal cities and towns. Unlike the other scenarios, this threat is already recognized by planners.
• Aerosol Effect: Global averages could also be increased by about 0.75C if pollution from industry is sharply cut. This counterintuitive effect occurs because aerosol particles from fossil fuel combustion block sunlight from reaching the ground.

Planning for the Unthinkable

The severe models could be utilized in planning the building of long-term infrastructure, including new towns, power generation facilities and water management networks. Knowledge about these future hazards could also speed the push to reduce fossil fuel emissions.

The study created the extreme models using a combination of real-world events, computer simulations and scientific theory. The possibilities exclude potential global problems like the global food shortages and geopolitical instability.

The research was commissioned as part of a national adaptation planning initiative. Earlier reports have cautioned that too little consideration was being paid to high-consequence, low-probability risks.

The government's climate advisors has stated that the UK needs to "become resilient to moderate heating" and examine the risks for 4C. Past policy documents have been described as being "inadequate" by some observers.

An official statement commented: "The climate emergency is at the heart of our national priorities, both building resilience and establishing itself as a low-carbon economy. It is vital that the UK is resilient for the consequences."