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The gravest projected effects of the climate emergency for the UK have been outlined by scientists, ranging from a blistering 4C jump in average temperatures to a 6.5-foot increase in ocean levels. Another scenario envisions a plunge of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Extremes, Not Guarantees

These effects, some of which are associated with climate tipping points, are seen as unlikely but possible. The researchers stated that these models filled a gap in planning that had left the UK not ready for extreme outcomes.

"The severe weather events we have mapped are not forecasts, but they are plausible," commented Nigel Arnell who directed the study. "Britain has been formulating policy in the absence of the methods to assess catastrophic outcomes. We've now provided planners what they need to plan for future conditions they hope never happen, but dare not dismiss."

A Suite of Extreme Weather Scenarios

A further series of worst-case scenarios maps the possible scale of severe conditions between now and the close of the 2100s. These suggest that temperatures could soar in some months by up to 6C above historical levels, while rainfall could be 300% of normal levels.

The probability of the catastrophic events occurring could not be calculated due to unknown factors about what measures will be enacted to combat global warming and how the planet's climate will react. This approach was likened to security threat evaluations or resilience checks for economic stability.

Critical Scenario Details

• Severe Heating: Global temperatures soaring past 4C by 2100 could transpire if climate action fails or if vicious cycles such as the tropical forests becoming a net carbon source release its vast reserves of carbon. This would lead to severe and lengthy heatwaves and dry spells affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the North Atlantic current, is losing strength and losing stability due to global heating. A collapse commencing by 2030 would lead to a drastic cooling in the UK. "Farming would face immense difficulties and water resources would be fundamentally reshaped," said the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in Greenland and Antarctica collapse rapidly, inundating coastal cities and towns. Differing from the other scenarios, this possibility is already known by infrastructure experts.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because pollution particles from fossil fuel combustion scatter solar radiation from reaching the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be used to inform the building of critical national infrastructure, such as expanded cities, energy plants and urban drainage systems. Knowledge about these future hazards could also accelerate the drive to reduce greenhouse gas emissions.

The research created the worst-case scenarios using a combination of observed and historical experience, climate models and established principles. The possibilities exclude broader worldwide issues such as the devastation of food supplies and increased conflict.

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

The government's climate advisors has stated that the UK must "prepare for two degrees of warming" and evaluate the threats for 4C. Earlier government strategies have been labeled being "inadequate" by certain experts.

A national response noted: "The climate emergency is at the center of our national priorities, both adapting for the future and establishing itself as a renewable energy leader. It is crucial that the UK is resilient for the effects."