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The direst potential impacts of the global heating for the UK have been mapped by researchers, ranging from a scorching 4C rise in mean temperatures to a 2-metre rise in sea level. An alternative projection foresees a plunge of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset food production and energy demand.

Credible Events, Not Forecasts

These consequences, some of which are connected to climate tipping points, are considered as unlikely but credible. The scientists said that these models filled a gap in planning that had rendered the UK ill-prepared for extreme outcomes.

"The climate extremes we have outlined are not forecasts, but they are possible," stated Nigel Arnell who oversaw the analysis. "Britain has been formulating policy lacking the tools to test against catastrophic outcomes. We've now provided policymakers what they need to get ready for future conditions they wish to avoid, but can’t afford to ignore."

A Range of Severe Conditions Projections

Another collection of severe models details the possible scale of harsh climate between now and the year 2100. These indicate that temperatures could rocket in certain periods by up to 6C above historical levels, while precipitation could be three times standard measurements.

The probability of the extreme scenarios happening remains uncertain due to a lack of certainty about what measures will be implemented to address global warming and how the climate system will respond. This approach was compared to national security risk assessments or stress tests for the banking sector.

Major Scenario Details

• 4C Temperature Rise: Worldwide averages soaring past 4C by 2100 could occur if climate action fails or if strong feedback loops like the tropical forests dying emit its vast reserves of carbon. This would result in intense and enduring heat domes and water shortages plaguing the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is slowing down and becoming unstable due to global heating. A full shutdown beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would struggle enormously and water resources would be drastically changed," said Arnell.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in Greenland and Antarctica melt abruptly, inundating low-lying areas. In contrast to the other scenarios, this possibility is already recognized by infrastructure experts.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if airborne particulates is rapidly cleaned up. This counterintuitive effect occurs because pollution particles from fossil fuel combustion block sunlight from reaching the ground.

Planning for the Worst

The severe models could be used to inform the development of major projects, including housing developments, power generation facilities and urban drainage systems. Knowledge about these environmental threats could also hasten the drive to cut fossil fuel emissions.

The analysis developed the extreme models using a mix of observed and historical experience, climate models and established principles. The scenarios omit broader worldwide issues like the devastation of food supplies and increased conflict.

The project was commissioned as part of a national risk assessment framework. Previous assessments have warned that too little consideration was being given to catastrophic yet improbable risks.

Official experts has stated that the UK needs to "adapt to 2C" and assess the threats for four degrees. Previous adaptation plans have been described as being "very weak" by certain experts.

A national response commented: "Climate change is at the heart of this government’s agenda, both adapting for the future and becoming a low-carbon economy. It is essential that the UK is ready for the effects."