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The gravest possible consequences of the climate emergency for the UK have been outlined by experts, ranging from a blistering 4C rise in average temperatures to a two-metre increase in ocean levels. Another scenario predicts a drop of 6C in temperature following the collapse of crucial Atlantic Ocean currents, which would profoundly upset agriculture and energy demand.

Plausible Extremes, Not Predictions

These consequences, some of which are linked to climate tipping points, are considered as low probability but plausible. The researchers said that these projections filled a gap in risk assessment that had rendered the UK ill-prepared for extreme outcomes.

"The severe weather events we have outlined should not be seen as certainties, but they are plausible," said the professor who oversaw the analysis. "The UK has been planning lacking the methods to plan for catastrophic outcomes. We've now provided policymakers what they need to plan for environmental results they hope never happen, but can’t afford to ignore."

A Spectrum of Extreme Weather Scenarios

Another collection of dire projections details the possible scale of severe conditions between now and the end of the century. These suggest that temperatures could rocket in particular seasons by up to 6C higher than historical levels, while rainfall could be three times typical amounts.

The chance of the extreme scenarios coming to pass cannot be precisely determined due to a lack of certainty about what measures will be enacted to tackle global heating and how the Earth's systems will behave. This research was likened to defence planning or resilience checks for the banking sector.

Key Scenario Details

• Four-Degree Warming: Global temperatures soaring past 4C by 2100 could transpire if climate action breaks down or if vicious cycles such as the tropical forests dying release its enormous store of carbon. This would lead to intense and enduring heat domes and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the AMOC, is losing strength and becoming unstable due to climate change. A full shutdown beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would face immense difficulties and water resources would be completely altered," noted Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in the polar regions disintegrate quickly, inundating coastal cities and towns. Differing from the other scenarios, this threat is already recognized by coastal engineers.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if industrial aerosols is drastically reduced. This counterintuitive effect occurs because aerosol particles from industrial activity block solar radiation from reaching the ground.

Preparing for the Unthinkable

These dire projections could be applied to guide the building of critical national infrastructure, such as new towns, power generation facilities and water management networks. Knowledge about these future hazards could also hasten the transition to slash greenhouse gas emissions.

The study developed the extreme models using a combination of observed and historical experience, climate models and climate physics. The scenarios exclude international cascading effects like the global food shortages and increased conflict.

This work was requested as part of a national adaptation planning initiative. Independent analyses have cautioned that insufficient focus was being paid to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK must "adapt to 2C" and examine the threats for severe warming. Past policy documents have been labeled being "inadequate" by certain experts.

A national response said: "The climate emergency is at the core of our national priorities, both preparing for impacts and establishing itself as a renewable energy leader. It is crucial that the UK is resilient for the consequences."