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The gravest possible consequences of the climate emergency for the UK have been outlined by experts, including a blistering 4C rise in average temperatures to a 2-metre rise in ocean levels. An alternative projection foresees a drop of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would severely impact agriculture and energy demand.

Plausible Events, Not Predictions

These consequences, certain ones are associated with climate tipping points, are seen as improbable but plausible. The team stated that these projections addressed a shortfall in forecasting that had rendered the UK not ready for worst-case results.

"The severe weather events we have outlined should not be seen as certainties, but they are possible," said the professor who led the analysis. "The nation has been planning without the frameworks to plan for worst-case scenarios. We've now provided policymakers what they need to get ready for future conditions they hope never happen, but must not overlook."

A Suite of Extreme Weather Possibilities

A second set of dire projections details the projected severity of severe conditions between now and the close of the 2100s. These indicate that thermometer readings could rocket in certain periods by up to 6C higher than the norm, while rainfall could be 300% of typical amounts.

The chance of the catastrophic events happening cannot be precisely determined due to a lack of certainty about what steps will be enacted to address global heating and how the planet's climate will behave. This research was compared to defence planning or resilience checks for financial systems.

Major Outcome Details

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could transpire if emissions cuts breaks down or if powerful amplifying effects like the Amazon rainforest dying unleash its enormous store of carbon. This would result in extreme and prolonged heat domes and dry spells plaguing the UK in summer.
• Ocean Circulation Failure: A major ocean current, the AMOC, is slowing down and losing stability due to climate change. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Crop production would face immense difficulties and water supplies would be fundamentally reshaped," noted Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic melt abruptly, inundating coastal cities and towns. Differing from the other scenarios, this risk is already recognized by infrastructure experts.
• Clean Air Warming: Global averages could also be increased by about 0.75C if pollution from industry is rapidly cleaned up. This unexpected result occurs because pollution particles from burning coal reflect solar radiation from warming the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be used to inform the construction of long-term infrastructure, such as expanded cities, energy plants and water management networks. Understanding these climate risks could also accelerate the transition to slash fossil fuel emissions.

The study created the severe projections using a blend of observed and historical experience, digital projections and scientific theory. These outcomes exclude international cascading effects including the devastation of food supplies and increased conflict.

The research was requested as part of a government’s adaptation planning initiative. Previous assessments have stated that insufficient focus was being allocated to low‐likelihood but high‐impact risks.

An independent advisory body has stated that the UK needs to "prepare for two degrees of warming" and assess the risks for four degrees. Previous adaptation plans have been criticised as being "insufficient" by environmental groups.

A government spokesperson said: "Global warming is at the core 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 effects."