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The most severe possible consequences of the climate emergency for the UK have been outlined by researchers, encompassing a blistering 4C increase in average temperatures to a two-metre surge in sea levels. An alternative projection predicts a drop of 6C in temperatures following the failure of key Atlantic Ocean currents, which would massively disrupt farming and energy demand.

Credible Outcomes, Not Guarantees

These consequences, a number of which are connected to irreversible climate shifts, are viewed as unlikely but plausible. The team said that these projections filled a gap in risk assessment that had rendered the UK ill-prepared for extreme outcomes.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are possible," said the professor who oversaw the study. "The nation has been planning lacking the frameworks to plan for extreme possibilities. We've now given planners what they need to get ready for environmental results they pray never occur, but dare not dismiss."

A Spectrum of Harsh Climate Projections

Another collection of dire projections details the potential extent of extreme weather between now and the close of the 2100s. These show that temperatures could rocket in particular seasons by up to 6C above average, while precipitation could be three times standard measurements.

The likelihood of the worst-case outcomes coming to pass could not be calculated due to a lack of certainty about what measures will be enacted to combat global warming and how the climate system will behave. This analysis was compared to national security risk assessments or stress tests for economic stability.

Major Outcome Elements

• Four-Degree Warming: Worldwide averages soaring past 4C by 2100 could occur if international cooperation fails or if powerful amplifying effects like the Amazon rainforest dying unleash its vast reserves of carbon. This would lead to extreme and prolonged heat domes and dry spells plaguing the UK in summer.
• Atlantic Current Collapse: A key circulation system, the North Atlantic current, is slowing down and becoming unstable due to ocean warming. A full shutdown starting around 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and freshwater availability would be drastically changed," said Arnell.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in Greenland and Antarctica collapse rapidly, inundating seaside communities. Differing from the other scenarios, this possibility is already understood by infrastructure experts.
• Aerosol Effect: Temperatures could also be pushed higher by about 0.75C if airborne particulates is sharply cut. This unexpected result occurs because tiny specks from burning coal block solar radiation from reaching the ground.

Planning for the Worst

The severe models could be utilized in planning the building of critical national infrastructure, for example expanded cities, energy plants and water management networks. Awareness of these climate risks could also accelerate the transition to reduce greenhouse gas emissions.

The analysis formulated the worst-case scenarios using a combination of past data and records, climate models and established principles. The possibilities exclude potential global problems including the agricultural collapse and increased conflict.

The research was commissioned as part of a national adaptation planning initiative. Earlier reports have stated that insufficient focus was being paid to catastrophic yet improbable risks.

An independent advisory body has said that the UK needs to "become resilient to moderate heating" and examine the dangers for four degrees. Past policy documents have been described as being "inadequate" by environmental groups.

A national response said: "Global warming is at the center of this government’s agenda, both building resilience and establishing itself as a clean energy superpower. It is crucial that the UK is prepared for the effects."