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The most severe potential impacts of the climate emergency for the UK have been detailed by experts, ranging from a searing 4C jump 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 farming and energy demand.

Plausible Events, Not Forecasts

These effects, certain ones are linked to climate tipping points, are viewed as low probability but plausible. The team explained that these models addressed a shortfall in risk assessment that had left the UK ill-prepared for extreme outcomes.

"The worst-case scenarios we have detailed aren’t predictions, but they are possible," commented Nigel Arnell who oversaw the analysis. "Britain has been planning in the absence of the tools to plan for worst-case scenarios. We've now supplied decision-makers what they need to prepare for climate outcomes they wish to avoid, but can’t afford to ignore."

A Suite of Harsh Climate Projections

Another collection of worst-case scenarios maps the potential extent of harsh climate between now and the end of the century. These suggest that thermometer readings could rocket in particular seasons by up to 6C higher than the norm, while precipitation could be 300% of typical amounts.

The chance of the worst-case outcomes coming to pass remains uncertain due to unknown factors about what action will be enacted to address global warming and how the planet's climate will react. This analysis was described as similar to defence planning or scenario planning for the banking sector.

Major Scenario Details

• 4C Temperature Rise: Planetary heating rising well above 4C by 2100 could transpire if international cooperation collapses or if vicious cycles like the Amazon rainforest perishing emit its huge repository of carbon. This would result in severe and lengthy heat domes and dry spells hitting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is weakening and becoming unstable due to climate change. A full shutdown starting around 2030 would lead to a 6C cooling in the UK. "Farming would struggle enormously and water supplies would be completely altered," said Arnell.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica melt abruptly, submerging low-lying areas. In contrast to the other scenarios, this risk is already understood by coastal engineers.
• Aerosol Effect: Temperatures could also be pushed higher by about 0.75C if pollution from industry is sharply cut. This counterintuitive effect occurs because pollution particles from burning coal reflect solar radiation from warming the ground.

Planning for the Extreme

The worst-case scenarios could be used to inform the development of critical national infrastructure, including new towns, power generation facilities and water management networks. Awareness of these environmental threats could also accelerate the push to reduce carbon pollution.

The research created the worst-case scenarios using a blend of observed and historical experience, digital projections and established principles. These outcomes omit broader worldwide issues including the agricultural collapse and geopolitical instability.

The research was initiated as part of a government’s risk assessment framework. Earlier reports have warned that insufficient focus was being allocated to high-consequence, low-probability risks.

The government's climate advisors has stated that the UK needs to "adapt to 2C" and assess the dangers for severe warming. Past policy documents have been described as being "very weak" by certain experts.

A government spokesperson noted: "Climate change is at the heart of the country's focus, both preparing for impacts and transitioning to a low-carbon economy. It is essential that the UK is prepared for the consequences."