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The direst possible consequences of the climate crisis for the UK have been detailed by scientists, including a scorching 4C rise in mean temperatures to a two-metre rise in sea level. An alternative projection envisions a plunge of 6C in temperatures following the collapse of critical Atlantic Ocean currents, which would severely impact food production and energy needs.

Credible Events, Not Predictions

These impacts, some of which are linked to climate tipping points, are considered as low probability but possible. The scientists said that these models addressed a shortfall in planning that had left the UK not ready for catastrophic possibilities.

"The climate extremes we have outlined are not forecasts, but they are credible," commented Nigel Arnell who directed the study. "Britain has been making preparations lacking the tools to plan for extreme possibilities. We've now given decision-makers what they need to prepare for climate outcomes they wish to avoid, but must not overlook."

A Range of Harsh Climate Projections

Another collection of dire projections maps the possible scale of extreme weather between now and the year 2100. These show that temperatures could skyrocket in some months by up to 6C above average, while rainfall could be 300% of typical amounts.

The likelihood of the worst-case outcomes coming to pass remains uncertain due to a lack of certainty about what steps will be enacted to tackle global warming and how the planet's climate will respond. This analysis was described as similar to national security risk assessments or resilience checks for the banking sector.

Major Scenario Highlights

• Four-Degree Warming: Global temperatures rising well above 4C by 2100 could happen if international cooperation collapses or if powerful amplifying effects including the Amazon basin becoming a net carbon source emit its enormous store of carbon. This would cause severe and lengthy heat domes and droughts affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is slowing down and showing signs of collapse due to ocean warming. A collapse starting around 2030 would lead to a drastic cooling in the UK. "Crop production would struggle enormously and freshwater availability would be completely altered," explained Arnell.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the polar regions collapse rapidly, inundating coastal cities and towns. Unlike the other scenarios, this risk is already understood by coastal engineers.
• Clean Air Warming: Global averages could also be increased by about 0.75C if industrial aerosols is sharply cut. This unexpected result occurs because aerosol particles from industrial activity block sunlight from warming the ground.

Building Resilience Against the Worst

The worst-case scenarios could be utilized in planning the development of critical national infrastructure, such as expanded cities, energy plants and urban drainage systems. Knowledge about these environmental threats could also speed the push to slash greenhouse gas emissions.

The research created the severe projections using a blend of real-world events, computer simulations and established principles. The scenarios do not take into account international cascading effects including the agricultural collapse and increased conflict.

This work was requested as part of a government’s adaptation planning initiative. Earlier reports have warned that too little consideration was being allocated to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK must "become resilient to moderate heating" and assess the dangers for severe warming. Past policy documents have been criticised as being "inadequate" by some observers.

An official statement said: "Climate change is at the core of our national priorities, both building resilience and transitioning to a renewable energy leader. It is essential that the UK is ready for the consequences."