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The most severe potential impacts of the climate emergency for the UK have been mapped by scientists, including a searing 4C increase in average temperatures to a 6.5-foot surge in sea levels. Another scenario predicts a decline of 6C in temperatures following the failure of key Atlantic Ocean currents, which would severely impact farming and energy demand.

Credible Extremes, Not Forecasts

These consequences, a number of which are linked to irreversible climate shifts, are seen as low probability but possible. The scientists explained that these projections addressed a shortfall in planning that had left the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined are not forecasts, but they are possible," said Nigel Arnell who oversaw the research. "Britain has been making preparations lacking the tools to test against worst-case scenarios. We've now supplied planners what they need to prepare for future conditions they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Scenarios

A further series of dire projections details the possible scale of harsh climate between now and the year 2100. These show that thermometer readings could rocket in certain periods by up to 6C higher than the norm, while precipitation could be triple standard measurements.

The chance of the extreme scenarios coming to pass cannot be precisely determined due to uncertainty about what steps will be enacted to tackle global warming and how the Earth's systems will react. This approach was compared to defence planning or scenario planning for economic stability.

Critical Possibility Elements

• Severe Heating: Global temperatures exceeding 4C by 2100 could happen if international cooperation fails or if powerful amplifying effects such as the Amazon rainforest becoming a net carbon source unleash its huge repository of carbon. This would cause intense and enduring heat domes and water shortages affecting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the North Atlantic current, is losing strength and becoming unstable due to climate change. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and water supplies would be fundamentally reshaped," explained Arnell.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions melt abruptly, flooding seaside communities. In contrast to the other scenarios, this threat is already recognized by planners.
• Aerosol Effect: Global averages could also be increased by about 0.75C if airborne particulates is sharply cut. This unexpected result occurs because aerosol particles from industrial activity scatter solar radiation from warming the ground.

Preparing for the Unthinkable

These dire projections could be used to inform the building of long-term infrastructure, including housing developments, energy plants and urban drainage systems. Understanding these environmental threats could also accelerate the push to slash carbon pollution.

The research created the worst-case scenarios using a mix of real-world events, digital projections and climate physics. The possibilities exclude international cascading effects such as the agricultural collapse and increased conflict.

This work was commissioned as part of a government’s adaptation planning initiative. Independent analyses have cautioned that too little consideration was being given to low‐likelihood but high‐impact risks.

Official experts has said that the UK must "prepare for two degrees of warming" and evaluate the dangers for 4C. Previous adaptation plans have been labeled being "insufficient" by certain experts.

A government spokesperson said: "The climate emergency is at the heart of this government’s agenda, both adapting for the future and establishing itself as a clean energy superpower. It is vital that the UK is ready for the consequences."