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The gravest potential impacts of the climate emergency for the UK have been mapped by scientists, including a blistering 4C rise in temperatures to a 6.5-foot increase in sea levels. A separate possibility foresees a decline of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would massively disrupt farming and energy needs.

Possible Outcomes, Not Guarantees

These impacts, certain ones are associated with irreversible climate shifts, are seen as low probability but credible. The scientists stated that these models addressed a shortfall in forecasting that had rendered the UK unprepared for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are credible," commented Nigel Arnell who led the study. "The UK has been making preparations in the absence of the frameworks to assess catastrophic outcomes. We've now supplied planners what they need to plan for environmental results they wish to avoid, but must not overlook."

A Suite of Severe Conditions Possibilities

A further series of severe models sets out the potential extent of severe conditions between now and the year 2100. These show that temperatures could rocket in some months by up to 6C higher than the norm, while rainfall could be 300% of typical amounts.

The probability of the extreme scenarios occurring remains uncertain due to unknown factors about what action will be enacted to combat global warming and how the Earth's systems will behave. This analysis was described as similar to national security risk assessments or resilience checks for financial systems.

Key Possibility Elements

• 4C Temperature Rise: Global temperatures exceeding 4C by 2100 could transpire if climate action fails or if powerful amplifying effects such as the Amazon rainforest perishing unleash its vast reserves of carbon. This would lead to extreme and prolonged heatwaves and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the AMOC, is weakening and becoming unstable due to ocean warming. 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 drastically changed," noted Arnell.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the polar regions melt abruptly, submerging low-lying areas. Differing from the other scenarios, this risk is already understood by coastal engineers.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if airborne particulates is rapidly cleaned up. This paradoxical outcome occurs because tiny specks from industrial activity scatter solar radiation from warming the ground.

Building Resilience Against the Worst

The worst-case scenarios could be applied to guide the building of long-term infrastructure, such as housing developments, power generation facilities and flood defences. Awareness of these climate risks could also hasten the transition to cut fossil fuel emissions.

The research created the worst-case scenarios using a mix of past data and records, computer simulations and scientific theory. The possibilities exclude international cascading effects such as the agricultural collapse and increased conflict.

This work was commissioned as part of a government’s adaptation planning initiative. Independent analyses have warned that not enough attention was being paid to low‐likelihood but high‐impact risks.

Official experts has said that the UK must "become resilient to moderate heating" and assess the dangers for 4C. Previous adaptation plans have been described as being "insufficient" by some observers.

An official statement said: "Climate change is at the heart of this government’s agenda, both adapting for the future and becoming a renewable energy leader. It is crucial that the UK is prepared for the effects."