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The gravest potential impacts of the climate emergency for the UK have been detailed by scientists, including a searing 4C increase in temperatures to a two-metre increase in sea level. Another scenario predicts a decline of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Possible Events, Not Predictions

These consequences, a number of which are linked to irreversible climate shifts, are seen as unlikely but credible. The team explained that these models plugged a hole in planning that had left the UK not ready for worst-case results.

"The climate extremes we have detailed should not be seen as certainties, but they are plausible," stated the lead researcher who oversaw the analysis. "The nation has been planning in the absence of the frameworks to test against extreme possibilities. We've now given planners what they need to plan for climate outcomes they hope never happen, but dare not dismiss."

A Suite of Extreme Weather Projections

Another collection of severe models details the potential extent of severe conditions between now and the year 2100. These suggest that temperatures could soar in certain periods by up to 6C above historical levels, while rainfall could be triple normal levels.

The chance of the catastrophic events happening could not be calculated due to a lack of certainty about what measures will be taken to combat climate change and how the climate system will react. This research was compared to security threat evaluations or scenario planning for the banking sector.

Key Possibility Highlights

• Severe Heating: Planetary heating soaring past 4C by 2100 could happen if emissions cuts fails or if powerful amplifying effects like the Amazon basin dying emit its vast reserves of carbon. This would lead to extreme and prolonged heatwaves and dry spells affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is weakening and becoming unstable due to global heating. A collapse beginning in 2030 would lead to a drastic cooling in the UK. "Crop production would be severely challenged and water supplies would be completely altered," said Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the Arctic and Antarctic collapse rapidly, submerging coastal cities and towns. In contrast to the other scenarios, this threat is already recognized by infrastructure experts.
• Aerosol Effect: Global averages could also be increased by about 0.75C if airborne particulates is rapidly cleaned up. This unexpected result occurs because aerosol particles from burning coal reflect solar radiation from reaching the ground.

Planning for the Worst

The worst-case scenarios could be used to inform the development of critical national infrastructure, including new towns, power generation facilities and flood defences. Knowledge about these climate risks could also hasten the transition to cut greenhouse gas emissions.

The analysis created the extreme models using a blend of observed and historical experience, climate models and established principles. These outcomes do not take into account potential global problems including the global food shortages and geopolitical instability.

The project was requested as part of a official adaptation planning initiative. Independent analyses have warned that not enough attention was being paid to high-consequence, low-probability risks.

Official experts has recommended that the UK must "become resilient to moderate heating" and assess the dangers for severe warming. Past policy documents have been criticised as being "inadequate" by certain experts.

A national response commented: "Global warming is at the center of this government’s agenda, both preparing for impacts and becoming a low-carbon economy. It is essential that the UK is ready for the impacts."