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The direst potential impacts of the climate crisis for the UK have been detailed by scientists, ranging from a scorching 4C increase in mean temperatures to a 6.5-foot surge in sea level. A separate possibility predicts a drop of 6C in temperatures following the failure of critical Atlantic Ocean currents, which would massively disrupt farming and energy demand.

Plausible Events, Not Guarantees

These effects, a number of which are linked to irreversible climate shifts, are seen as improbable but credible. The team said that these models filled a gap in forecasting that had rendered the UK not ready for catastrophic possibilities.

"The worst-case scenarios we have mapped should not be seen as certainties, but they are credible," stated Nigel Arnell who led the research. "The UK has been formulating policy without the methods to assess catastrophic outcomes. We've now provided policymakers what they need to plan for future conditions they pray never occur, but can’t afford to ignore."

A Range of Harsh Climate Scenarios

A second set of dire projections details the potential extent of harsh climate between now and the close of the 2100s. These show that temperatures could rocket in some months by up to 6C higher than historical levels, while precipitation could be triple standard measurements.

The chance of the catastrophic events happening remains uncertain due to a lack of certainty about what action will be implemented to combat climate change and how the Earth's systems will behave. This analysis was compared to national security risk assessments or resilience checks for economic stability.

Critical Outcome Elements

• Four-Degree Warming: Worldwide averages soaring past 4C by 2100 could transpire if climate action fails or if powerful amplifying effects like the Amazon basin dying release its huge repository of carbon. This would result in intense and enduring heatwaves and droughts affecting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is weakening and losing stability due to global heating. A complete failure beginning in 2030 would lead to a drastic cooling in the UK. "Farming would be severely challenged and water resources would be completely altered," noted Arnell.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions melt abruptly, inundating low-lying areas. In contrast to the other scenarios, this threat is already known by planners.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if airborne particulates is rapidly cleaned up. This paradoxical outcome occurs because pollution particles from fossil fuel combustion block solar radiation from reaching the ground.

Preparing for the Unthinkable

These dire projections could be applied to guide the construction of major projects, including housing developments, nuclear power stations and urban drainage systems. Knowledge about these future hazards could also speed the drive to cut fossil fuel emissions.

The analysis created the worst-case scenarios using a mix of observed and historical experience, computer simulations and climate physics. The scenarios exclude international cascading effects like the agricultural collapse and resource wars.

This work was commissioned as part of a government’s climate resilience programme. Previous assessments have warned that insufficient focus was being paid to high-consequence, low-probability risks.

The government's climate advisors has stated that the UK needs to "become resilient to moderate heating" and assess the risks for four degrees. Previous adaptation plans have been described as being "very weak" by certain experts.

A national response commented: "The climate emergency is at the heart of our national priorities, both preparing for impacts and establishing itself as a clean energy superpower. It is vital that the UK is resilient for the impacts."