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The most severe potential impacts of the climate emergency for the UK have been mapped by experts, encompassing a blistering 4C increase in temperatures to a two-metre surge in sea level. A separate possibility predicts a decline of 6C in temperatures following the failure of crucial Atlantic Ocean currents, which would profoundly upset agriculture and energy needs.

Plausible Events, Not Forecasts

These effects, certain ones are connected to irreversible climate shifts, are seen as unlikely but plausible. The scientists said that these projections filled a gap in forecasting that had left the UK unprepared for extreme outcomes.

"The climate extremes we have mapped should not be seen as certainties, but they are credible," stated the professor who directed the research. "The UK has been making preparations lacking the tools to test against catastrophic outcomes. We've now supplied policymakers what they need to get ready for climate outcomes they wish to avoid, but can’t afford to ignore."

A Suite of Extreme Weather Projections

A second set of worst-case scenarios maps the possible scale of severe conditions between now and the close of the 2100s. These show that thermometer readings could rocket in particular seasons by up to 6C higher than the norm, while precipitation could be three times typical amounts.

The chance of the worst-case outcomes happening remains uncertain due to uncertainty about what action will be enacted to tackle global heating and how the climate system will behave. This analysis was described as similar to defence planning or scenario planning for economic stability.

Major Possibility Elements

• Four-Degree Warming: Global temperatures soaring past 4C by 2100 could occur if climate action fails or if strong feedback loops like the Amazon rainforest becoming a net carbon source release its huge repository of carbon. This would cause severe and lengthy heatwaves and dry spells affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is losing strength and losing stability due to global heating. A collapse starting around 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would struggle enormously and water resources would be drastically changed," explained Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in Greenland and Antarctica disintegrate quickly, flooding coastal cities and towns. In contrast to the other scenarios, this risk is already understood by planners.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This paradoxical outcome occurs because aerosol particles from burning coal block sunlight from reaching the ground.

Preparing for the Extreme

The worst-case scenarios could be applied to guide the development of major projects, including expanded cities, nuclear power stations and water management networks. Understanding these environmental threats could also accelerate the push to slash carbon pollution.

The research created the severe projections using a combination of past data and records, digital projections and scientific theory. These outcomes exclude potential global problems such as the agricultural collapse and geopolitical instability.

The project was commissioned as part of a government’s adaptation planning initiative. Independent analyses have warned that too little consideration was being paid to high-consequence, low-probability risks.

An independent advisory body has stated that the UK must "adapt to 2C" and examine the dangers for four degrees. Earlier government strategies have been criticised as being "inadequate" by some observers.

A government spokesperson commented: "The climate emergency is at the core of this government’s agenda, both preparing for impacts and establishing itself as a clean energy superpower. It is crucial that the UK is resilient for the effects."