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The direst potential impacts of the climate emergency for the UK have been mapped by researchers, encompassing a searing 4C rise in mean temperatures to a 6.5-foot increase in sea level. An alternative projection envisions a plunge of 6C in temperatures following the collapse of critical Atlantic Ocean currents, which would profoundly upset farming and power requirements.

Plausible Extremes, Not Forecasts

These consequences, a number of which are associated with climate tipping points, are viewed as unlikely but possible. The team stated that these models plugged a hole in risk assessment that had rendered the UK ill-prepared for catastrophic possibilities.

"The worst-case scenarios we have detailed aren’t predictions, but they are plausible," commented the professor who directed the study. "Britain has been formulating policy without the frameworks to test against extreme possibilities. We've now provided policymakers what they need to plan for climate outcomes they pray never occur, but dare not dismiss."

A Suite of Harsh Climate Scenarios

A further series of dire projections sets out the potential extent of severe conditions between now and the end of the century. These indicate that temperatures could skyrocket in some months by up to 6C higher than historical levels, while rainfall could be three times typical amounts.

The likelihood of the catastrophic events coming to pass cannot be precisely determined due to unknown factors about what steps will be implemented to tackle global heating and how the Earth's systems will respond. This approach was likened to defence planning or scenario planning for financial systems.

Critical Possibility Details

• 4C Temperature Rise: Planetary heating soaring past 4C by 2100 could happen if emissions cuts collapses or if powerful amplifying effects such as the tropical forests perishing release its vast reserves of carbon. This would lead to intense and enduring heat domes and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is losing strength and showing signs of collapse due to ocean warming. A full shutdown beginning in 2030 would lead to a drastic cooling in the UK. "Crop production would struggle enormously and water supplies would be completely altered," said Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the polar regions melt abruptly, submerging coastal cities and towns. In contrast to the other scenarios, this threat is already recognized by infrastructure experts.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if industrial aerosols is sharply cut. This counterintuitive effect occurs because pollution particles from industrial activity block sunlight from reaching the ground.

Preparing for the Worst

The severe models could be used to inform the development of long-term infrastructure, for example expanded cities, energy plants and water management networks. Knowledge about these climate risks could also speed the drive to cut greenhouse gas emissions.

The study formulated the severe projections using a mix of observed and historical experience, climate models and established principles. These outcomes omit potential global problems such as the devastation of food supplies and increased conflict.

This work was commissioned as part of a official adaptation planning initiative. Previous assessments have cautioned that too little consideration was being given to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK must "adapt to 2C" and evaluate the threats for four degrees. Past policy documents have been described as being "inadequate" by environmental groups.

A government spokesperson said: "Climate change is at the heart of this government’s agenda, both preparing for impacts and transitioning to a renewable energy leader. It is essential that the UK is resilient for the impacts."