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The direst possible consequences of the global heating for the UK have been outlined by researchers, encompassing a searing 4C jump in average temperatures to a 2-metre increase in sea level. An alternative projection foresees a drop of 6C in temperatures following the failure of critical Atlantic Ocean currents, which would massively disrupt food production and power requirements.

Plausible Outcomes, Not Guarantees

These consequences, certain ones are associated with irreversible climate shifts, are viewed as unlikely but credible. The researchers stated that these projections plugged a hole in planning that had rendered the UK not ready for worst-case results.

"The worst-case scenarios we have detailed are not forecasts, but they are possible," commented Nigel Arnell who led the study. "Britain has been making preparations in the absence of the tools to plan for catastrophic outcomes. We've now provided planners what they need to prepare for environmental results they hope never happen, but must not overlook."

A Spectrum of Severe Conditions Scenarios

Another collection of worst-case scenarios details the potential extent of harsh climate between now and the end of the century. These suggest that temperatures could rocket in certain periods by up to 6C higher than historical levels, while precipitation could be three times normal levels.

The probability of the worst-case outcomes coming to pass cannot be precisely determined due to unknown factors about what steps will be taken to combat global heating and how the climate system will behave. This research was likened to national security risk assessments or resilience checks for economic stability.

Critical Scenario Elements

• 4C Temperature Rise: Global temperatures exceeding 4C by 2100 could occur if climate action breaks down or if strong feedback loops including the tropical forests perishing release its huge repository of carbon. This would result in extreme and prolonged heat domes and dry spells affecting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the North Atlantic current, is slowing down and becoming unstable due to climate change. A complete failure beginning in 2030 would lead to a 6C cooling in the UK. "Crop production would struggle enormously and freshwater availability would be completely altered," said the professor.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the polar regions collapse rapidly, flooding seaside communities. Unlike the other scenarios, this threat is already known by coastal engineers.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if pollution from industry is drastically reduced. This paradoxical outcome occurs because tiny specks from fossil fuel combustion reflect solar radiation from warming the ground.

Building Resilience Against the Unthinkable

These dire projections could be utilized in planning the building of long-term infrastructure, for example new towns, energy plants and flood defences. Awareness of these future hazards could also hasten the push to slash fossil fuel emissions.

The research developed the extreme models using a combination of observed and historical experience, computer simulations and scientific theory. The scenarios omit international cascading effects like the agricultural collapse and resource wars.

The project was requested as part of a government’s climate resilience programme. Previous assessments have warned that not enough attention was being allocated to low‐likelihood but high‐impact risks.

The government's climate advisors 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 "insufficient" by certain experts.

A national response said: "The climate emergency is at the center of this government’s agenda, both adapting for the future and establishing itself as a clean energy superpower. It is crucial that the UK is resilient for the impacts."