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The direst potential impacts of the climate emergency for the UK have been mapped by experts, encompassing a searing 4C jump in average temperatures to a two-metre rise in ocean levels. A separate possibility predicts a plunge of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Possible Events, Not Guarantees

These effects, certain ones are linked to climate tipping points, are considered as unlikely but plausible. The researchers said that these scenarios plugged a hole in forecasting that had rendered the UK unprepared for catastrophic possibilities.

"The worst-case scenarios we have detailed should not be seen as certainties, but they are plausible," said the lead researcher who oversaw the research. "The UK has been planning without the frameworks to test against catastrophic outcomes. We've now provided decision-makers what they need to get ready for future conditions they hope never happen, but can’t afford to ignore."

A Spectrum of Extreme Weather Possibilities

A second set of worst-case scenarios maps the potential extent of severe conditions between now and the year 2100. These suggest that thermometer readings could rocket in particular seasons by up to 6C higher than the norm, while precipitation could be triple typical amounts.

The likelihood of the catastrophic events happening remains uncertain due to unknown factors about what steps will be implemented to address global heating and how the Earth's systems will react. This research was compared to national security risk assessments or resilience checks for economic stability.

Critical Scenario Details

• Four-Degree Warming: Worldwide averages exceeding 4C by 2100 could transpire if climate action collapses or if powerful amplifying effects including the tropical forests dying release its vast reserves of carbon. This would cause extreme and prolonged heatwaves and water shortages plaguing the UK in summer.
• AMOC Shutdown: A major ocean current, the AMOC, is losing strength and showing signs of collapse due to ocean warming. A complete failure starting around 2030 would lead to a 6C cooling in the UK. "Crop production would face immense difficulties and water supplies would be fundamentally reshaped," explained the professor.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the polar regions melt abruptly, submerging low-lying areas. Unlike the other scenarios, this risk 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 unexpected result occurs because aerosol particles from burning coal block sunlight from reaching the ground.

Preparing for the Extreme

The severe models could be applied to guide the construction of major projects, for example new towns, nuclear power stations and flood defences. Knowledge about these climate risks could also accelerate the drive to cut greenhouse gas emissions.

The research developed the worst-case scenarios using a blend of real-world events, computer simulations and established principles. The scenarios exclude potential global problems like the global food shortages and increased conflict.

The project was requested as part of a official climate resilience programme. Independent analyses have stated that too little consideration was being paid to catastrophic yet improbable risks.

Official experts has said that the UK must "adapt to 2C" and assess the risks for severe warming. Earlier government strategies have been criticised as being "very weak" by certain experts.

A national response commented: "Global warming is at the heart of this government’s agenda, both adapting for the future and establishing itself as a low-carbon economy. It is vital that the UK is ready for the consequences."