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The gravest potential impacts of the global heating for the UK have been mapped by researchers, ranging from a searing 4C jump in mean temperatures to a two-metre increase in sea levels. A separate possibility foresees a drop of 6C in temperatures following the collapse of crucial Atlantic Ocean currents, which would profoundly upset agriculture and power requirements.

Plausible Outcomes, Not Predictions

These impacts, a number of which are connected to irreversible climate shifts, are seen as unlikely but plausible. The team said that these projections filled a gap in forecasting that had rendered the UK unprepared for extreme outcomes.

"The severe weather events we have mapped should not be seen as certainties, but they are plausible," said the professor who led the analysis. "The nation has been formulating policy without the methods to test against worst-case scenarios. We've now provided policymakers what they need to prepare for environmental results they wish to avoid, but can’t afford to ignore."

A Range of Extreme Weather Projections

Another collection of dire projections details the possible scale of harsh climate between now and the close of the 2100s. These indicate that thermometer readings could soar in particular seasons by up to 6C higher than historical levels, while precipitation could be triple typical amounts.

The chance of the extreme scenarios happening cannot be precisely determined due to unknown factors about what action will be taken to tackle global heating and how the planet's climate will respond. This approach was described as similar to national security risk assessments or resilience checks for financial systems.

Critical Outcome Elements

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could transpire if emissions cuts fails or if strong feedback loops such as the tropical forests perishing unleash its enormous store of carbon. This would cause intense and enduring heatwaves and dry spells plaguing the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is weakening and becoming unstable due to climate change. A complete failure starting around 2030 would lead to a 6C cooling in the UK. "Crop production would be severely challenged and freshwater availability would be completely altered," said Arnell.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the polar regions melt abruptly, submerging coastal cities and towns. Differing from the other scenarios, this threat is already understood by infrastructure experts.
• Clean Air Warming: Temperatures could also be increased by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because pollution particles from burning coal scatter sunlight from warming the ground.

Preparing for the Worst

The severe models could be used to inform the building of major projects, such as new towns, power generation facilities and urban drainage systems. Knowledge about these climate risks could also speed the transition to reduce carbon pollution.

The analysis created the extreme models using a mix of past data and records, computer simulations and established principles. The possibilities exclude international cascading effects including the agricultural collapse and resource wars.

The research was commissioned as part of a national risk assessment framework. Previous assessments have stated that not enough attention was being given to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "become resilient to moderate heating" and evaluate the risks for four degrees. Past policy documents have been described as being "inadequate" by some observers.

An official statement noted: "Global warming is at the core of the country's focus, both adapting for the future and becoming a clean energy superpower. It is crucial that the UK is ready for the impacts."