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The gravest projected effects of the climate emergency for the UK have been mapped by experts, ranging from a searing 4C rise in temperatures to a 2-metre rise in sea level. An alternative projection envisions a plunge of 6C in temperature following the failure of key Atlantic Ocean currents, which would severely impact agriculture and energy demand.

Credible Events, Not Predictions

These effects, some of which are connected to climate tipping points, are seen as low probability but possible. The team explained that these scenarios addressed a shortfall in forecasting that had rendered the UK not ready for worst-case results.

"The severe weather events we have outlined aren’t predictions, but they are possible," said the professor who led the analysis. "Britain has been planning lacking the tools to test against catastrophic outcomes. We've now given policymakers what they need to plan for environmental results they hope never happen, but dare not dismiss."

A Suite of Extreme Weather Possibilities

Another collection of worst-case scenarios sets out the projected severity of harsh climate between now and the year 2100. These indicate that temperatures could skyrocket in particular seasons by up to 6C above the norm, while precipitation could be 300% of typical amounts.

The probability of the worst-case outcomes coming to pass remains uncertain due to uncertainty about what steps will be enacted to combat climate change and how the planet's climate will respond. This research was compared to defence planning or resilience checks for financial systems.

Major Possibility Details

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could occur if emissions cuts collapses or if vicious cycles including the tropical forests becoming a net carbon source unleash its vast reserves of carbon. This would result in intense and enduring heat domes and water shortages hitting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is losing strength and becoming unstable due to global heating. A full shutdown commencing by 2030 would lead to a 6C cooling in the UK. "Crop production would face immense difficulties and freshwater availability would be drastically changed," explained Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions collapse rapidly, inundating coastal cities and towns. In contrast to the other scenarios, this possibility is already known by infrastructure experts.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if airborne particulates is drastically reduced. This counterintuitive effect occurs because aerosol particles from burning coal block solar radiation from warming the ground.

Preparing for the Worst

The severe models could be used to inform the construction of major projects, including new towns, nuclear power stations and urban drainage systems. Knowledge about these future hazards could also accelerate the transition to reduce carbon pollution.

The analysis developed the worst-case scenarios using a blend of observed and historical experience, computer simulations and scientific theory. The scenarios do not take into account international cascading effects like the agricultural collapse and increased conflict.

The research was initiated as part of a government’s adaptation planning initiative. Independent analyses have stated that insufficient focus was being given to catastrophic yet improbable risks.

Official experts has said that the UK must "become resilient to moderate heating" and assess the risks for four degrees. Past policy documents have been labeled being "insufficient" by certain experts.

A government spokesperson noted: "Climate change is at the center of the country's focus, both building resilience and establishing itself as a renewable energy leader. It is vital that the UK is ready for the impacts."