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The direst projected effects of the global heating for the UK have been detailed by scientists, encompassing a searing 4C rise in temperatures to a two-metre rise in ocean levels. Another scenario envisions a plunge of 6C in temperatures following the shutdown of critical Atlantic Ocean currents, which would profoundly upset food production and power requirements.

Plausible Extremes, Not Predictions

These effects, certain ones are linked to climate tipping points, are viewed as unlikely but possible. The team explained that these scenarios addressed a shortfall in risk assessment that had left the UK unprepared for worst-case results.

"The worst-case scenarios we have detailed aren’t predictions, but they are credible," commented the professor who led the study. "Britain has been planning lacking the methods to test against catastrophic outcomes. We've now supplied planners what they need to prepare for climate outcomes they pray never occur, but can’t afford to ignore."

A Spectrum of Severe Conditions Projections

A further series of severe models maps the possible scale of harsh climate between now and the end of the century. These suggest that temperatures could soar in certain periods by up to 6C above average, while precipitation could be 300% of typical amounts.

The likelihood of the extreme scenarios occurring remains uncertain due to uncertainty about what action will be taken to address global warming and how the climate system will behave. This analysis was described as similar to national security risk assessments or stress tests for financial systems.

Major Outcome Elements

• Severe Heating: Global temperatures exceeding 4C by 2100 could transpire if climate action breaks down or if vicious cycles such as the Amazon rainforest perishing release its huge repository of carbon. This would cause intense and enduring heat domes and water shortages plaguing the UK in summer.
• Ocean Circulation Failure: A key circulation system, the AMOC, is losing strength and becoming unstable due to climate change. A complete failure beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and freshwater availability would be drastically changed," said Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the polar regions disintegrate quickly, flooding low-lying areas. Unlike the other scenarios, this possibility is already known by planners.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if industrial aerosols is drastically reduced. This paradoxical outcome occurs because aerosol particles from fossil fuel combustion reflect sunlight from reaching the ground.

Preparing for the Worst

The worst-case scenarios could be applied to guide the construction of critical national infrastructure, for example expanded cities, energy plants and urban drainage systems. Knowledge about these environmental threats could also hasten the transition to reduce fossil fuel emissions.

The analysis created the worst-case scenarios using a mix of observed and historical experience, computer simulations and established principles. The possibilities exclude international cascading effects like the devastation of food supplies and geopolitical instability.

This work was requested as part of a government’s adaptation planning initiative. Independent analyses have stated that not enough attention was being allocated to low‐likelihood but high‐impact risks.

The government's climate advisors has said that the UK must "prepare for two degrees of warming" and evaluate the dangers for severe warming. Earlier government strategies have been criticised as being "very weak" by some observers.

A government spokesperson noted: "Global warming is at the heart of this government’s agenda, both building resilience and becoming a low-carbon economy. It is vital that the UK is resilient for the effects."