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The gravest potential impacts of the climate emergency for the UK have been detailed by researchers, including a searing 4C jump in mean temperatures to a two-metre rise in sea levels. Another scenario predicts a drop of 6C in temperatures following the collapse of critical Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Credible Events, Not Guarantees

These impacts, some of which are connected to climate tipping points, are considered as unlikely but possible. The scientists explained that these scenarios filled a gap in risk assessment that had left the UK ill-prepared for worst-case results.

"The severe weather events we have mapped are not forecasts, but they are plausible," commented Nigel Arnell who led the analysis. "The nation has been making preparations in the absence of the methods to assess catastrophic outcomes. We've now supplied decision-makers what they need to prepare for climate outcomes they hope never happen, but dare not dismiss."

A Range of Severe Conditions Scenarios

A further series of severe models maps the possible scale of extreme weather between now and the end of the century. These show that thermometer readings could soar in particular seasons by up to 6C higher than average, while precipitation could be three times typical amounts.

The probability of the extreme scenarios occurring could not be calculated due to unknown factors about what steps will be implemented to address global heating and how the planet's climate will behave. This analysis was likened to defence planning or stress tests for financial systems.

Major Possibility Details

• 4C Temperature Rise: Global temperatures exceeding 4C by 2100 could occur if climate action fails or if vicious cycles such as the Amazon basin becoming a net carbon source emit its vast reserves of carbon. This would cause extreme and prolonged heat domes and dry spells affecting the UK in summer.
• AMOC Shutdown: A major ocean current, the North Atlantic current, is losing strength and becoming unstable due to ocean warming. A collapse beginning in 2030 would lead to a 6C cooling in the UK. "Farming would struggle enormously and freshwater availability would be drastically changed," noted Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica collapse rapidly, inundating seaside communities. In contrast to the other scenarios, this threat is already known by coastal engineers.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This unexpected result occurs because tiny specks from burning coal scatter solar radiation from warming the ground.

Building Resilience Against the Worst

The severe models could be utilized in planning the building of major projects, for example housing developments, nuclear power stations and flood defences. Understanding these climate risks could also hasten the transition to slash fossil fuel emissions.

The study formulated the severe projections using a mix of past data and records, computer simulations and established principles. The possibilities omit broader worldwide issues such as the devastation of food supplies and geopolitical instability.

This work was commissioned as part of a official adaptation planning initiative. Earlier reports have cautioned that not enough attention was being paid to low‐likelihood but high‐impact risks.

The government's climate advisors has recommended that the UK must "adapt to 2C" and assess the threats for 4C. Previous adaptation plans have been criticised as being "very weak" by environmental groups.

An official statement commented: "Global warming is at the core of the country's focus, both adapting for the future and becoming a low-carbon economy. It is essential that the UK is prepared for the consequences."