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The direst potential impacts of the climate crisis for the UK have been mapped by scientists, encompassing a searing 4C rise in temperatures to a 2-metre rise in ocean levels. An alternative projection foresees a decline of 6C in temperatures following the failure of key Atlantic Ocean currents, which would massively disrupt food production and energy needs.

Possible Events, Not Guarantees

These impacts, some of which are connected to climate tipping points, are seen as unlikely but possible. The scientists said that these projections plugged a hole in forecasting that had left the UK unprepared for catastrophic possibilities.

"The worst-case scenarios we have outlined aren’t predictions, but they are possible," commented the professor who oversaw the study. "The UK has been formulating policy in the absence of the tools to test against catastrophic outcomes. We've now given planners what they need to plan for climate outcomes they wish to avoid, but can’t afford to ignore."

A Range of Harsh Climate Projections

A further series of dire projections maps the potential extent of severe conditions between now and the year 2100. These suggest that temperatures could soar in some months by up to 6C higher than the norm, while precipitation could be triple typical amounts.

The likelihood of the extreme scenarios happening cannot be precisely determined due to a lack of certainty about what action will be taken to combat global heating and how the Earth's systems will react. This analysis was likened to security threat evaluations or stress tests for the banking sector.

Key Scenario Elements

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could happen if emissions cuts collapses or if vicious cycles such as the tropical forests becoming a net carbon source release its vast reserves of carbon. This would lead to extreme and prolonged heatwaves and dry spells plaguing the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is weakening and losing stability 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 resources would be completely altered," said Arnell.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the Arctic and Antarctic collapse rapidly, submerging seaside communities. In contrast to the other scenarios, this risk is already understood by coastal engineers.
• Pollution Paradox: Global averages could also be increased by about 0.75C if airborne particulates is sharply cut. This counterintuitive effect occurs because aerosol particles from industrial activity block solar radiation from reaching the ground.

Preparing for the Extreme

These dire projections could be applied to guide the construction of long-term infrastructure, including new towns, energy plants and water management networks. Awareness of these environmental threats could also speed the push to reduce carbon pollution.

The study created the extreme models using a combination of past data and records, digital projections and scientific theory. These outcomes exclude potential global problems such as the agricultural collapse and increased conflict.

The project was commissioned as part of a official adaptation planning initiative. Earlier reports have stated that too little consideration was being given to high-consequence, low-probability risks.

The government's climate advisors has said that the UK needs to "become resilient to moderate heating" and assess the dangers for severe warming. Past policy documents have been criticised as being "very weak" by certain experts.

An official statement commented: "Climate change is at the heart of the country's focus, both building resilience and transitioning to a renewable energy leader. It is crucial that the UK is resilient for the impacts."