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The gravest possible consequences of the global heating for the UK have been detailed by scientists, encompassing a scorching 4C jump in average temperatures to a two-metre increase in sea level. An alternative projection envisions a decline of 6C in temperatures following the failure of critical Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Extremes, Not Forecasts

These effects, some of which are associated with critical climate thresholds, are viewed as unlikely but possible. The researchers stated that these models plugged a hole in risk assessment that had left the UK unprepared for worst-case results.

"The severe weather events we have mapped should not be seen as certainties, but they are plausible," said the professor who directed the analysis. "The nation has been formulating policy without the frameworks to plan for extreme possibilities. We've now provided planners what they need to plan for climate outcomes they hope never happen, but dare not dismiss."

A Spectrum of Severe Conditions Possibilities

Another collection of severe models details the possible scale of harsh climate between now and the end of the century. These indicate that thermometer readings could skyrocket in certain periods by up to 6C above average, while precipitation could be 300% of standard measurements.

The probability of the extreme scenarios happening remains uncertain due to uncertainty about what measures will be taken to combat climate change and how the climate system will react. This analysis was likened to national security risk assessments or scenario planning for economic stability.

Critical Outcome Details

• 4C Temperature Rise: Global temperatures rising well above 4C by 2100 could happen if international cooperation collapses or if strong feedback loops such as the Amazon basin dying emit its vast reserves of carbon. This would result in extreme and prolonged heatwaves and droughts plaguing the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is weakening and becoming unstable due to ocean warming. A complete failure beginning in 2030 would lead to a six-degree temperature drop in the UK. "Crop production would face immense difficulties and water supplies would be drastically changed," explained Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic disintegrate quickly, inundating low-lying areas. In contrast to the other scenarios, this possibility 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 paradoxical outcome occurs because pollution particles from industrial activity block solar radiation from reaching the ground.

Preparing for the Worst

The severe models could be used to inform the building of major projects, for example housing developments, nuclear power stations and urban drainage systems. Knowledge about these future hazards could also speed the transition to cut fossil fuel emissions.

The research formulated the severe projections using a mix of real-world events, computer simulations and scientific theory. The scenarios do not take into account broader worldwide issues like the global food shortages and increased conflict.

The research was requested as part of a government’s adaptation planning initiative. Independent analyses have warned that too little consideration was being given to catastrophic yet improbable risks.

An independent advisory body has stated that the UK needs to "become resilient to moderate heating" and examine the threats for severe warming. Previous adaptation plans have been described as being "insufficient" by some observers.

An official statement said: "Climate change is at the heart of our national priorities, both preparing for impacts and becoming a low-carbon economy. It is vital that the UK is resilient for the consequences."