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The gravest possible consequences of the climate emergency for the UK have been mapped by researchers, including a scorching 4C increase in mean temperatures to a 6.5-foot increase in sea levels. Another scenario foresees a plunge of 6C in temperature following the collapse of key Atlantic Ocean currents, which would severely impact food production and power requirements.

Credible Events, Not Guarantees

These effects, a number of which are connected to climate tipping points, are viewed as unlikely but possible. The team explained that these projections addressed a shortfall in forecasting that had rendered the UK unprepared for extreme outcomes.

"The severe weather events we have outlined are not forecasts, but they are credible," said the professor who led the analysis. "Britain has been planning in the absence of the tools to plan for catastrophic outcomes. We've now provided decision-makers what they need to get ready for climate outcomes they pray never occur, but must not overlook."

A Suite of Harsh Climate Projections

Another collection of worst-case scenarios sets out the possible scale of severe conditions between now and the close of the 2100s. These suggest that temperatures could rocket in certain periods by up to 6C above average, while rainfall could be triple normal levels.

The probability of the worst-case outcomes happening cannot be precisely determined due to unknown factors about what steps will be taken to combat global warming and how the Earth's systems will respond. This analysis was described as similar to security threat evaluations or scenario planning for the banking sector.

Critical Outcome Highlights

• 4C Temperature Rise: Planetary heating rising well above 4C by 2100 could transpire if international cooperation breaks down or if powerful amplifying effects like the Amazon basin dying release its enormous store of carbon. This would lead to extreme and prolonged heat domes and water shortages plaguing the UK in summer.
• AMOC Shutdown: A major ocean current, the North Atlantic current, is weakening and losing stability due to global heating. A complete failure 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 surge of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the Arctic and Antarctic melt abruptly, flooding coastal cities and towns. Differing from the other scenarios, this risk is already understood by coastal engineers.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if industrial aerosols is sharply cut. This unexpected result occurs because tiny specks from fossil fuel combustion block solar radiation from reaching the ground.

Preparing for the Extreme

These dire projections could be applied to guide the building of long-term infrastructure, including expanded cities, energy plants and water management networks. Understanding these future hazards could also hasten the transition to cut carbon pollution.

The analysis formulated the severe projections using a blend of real-world events, computer simulations and scientific theory. These outcomes exclude international cascading effects including the global food shortages and resource wars.

The project was commissioned as part of a national adaptation planning initiative. Earlier reports have cautioned that insufficient focus was being paid to low‐likelihood but high‐impact risks.

The government's climate advisors has stated that the UK must "adapt to 2C" and assess the threats for 4C. Past policy documents have been labeled being "very weak" by environmental groups.

A national response noted: "Global warming is at the heart of our national priorities, both preparing for impacts and transitioning to a low-carbon economy. It is vital that the UK is resilient for the impacts."