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The direst potential impacts of the climate crisis for the UK have been mapped by experts, encompassing a searing 4C rise in average temperatures to a two-metre increase in sea levels. Another scenario foresees a plunge of 6C in temperature following the failure of key Atlantic Ocean currents, which would profoundly upset food production and power requirements.

Possible Extremes, Not Predictions

These effects, some of which are linked to irreversible climate shifts, are viewed as low probability but plausible. The team said that these scenarios addressed a shortfall in forecasting that had left the UK ill-prepared for catastrophic possibilities.

"The severe weather events we have detailed should not be seen as certainties, but they are plausible," commented Nigel Arnell who directed the research. "The nation has been planning in the absence of the tools to test against extreme possibilities. We've now provided planners what they need to plan for environmental results they hope never happen, but dare not dismiss."

A Spectrum of Severe Conditions Scenarios

A further series of worst-case scenarios sets out the projected severity of severe conditions between now and the year 2100. These show that thermometer readings could skyrocket in particular seasons by up to 6C higher than average, while rainfall could be 300% of standard measurements.

The likelihood of the worst-case outcomes happening could not be calculated due to a lack of certainty about what action will be enacted to tackle climate change and how the Earth's systems will respond. This analysis was compared to defence planning or resilience checks for financial systems.

Key Scenario Highlights

• Four-Degree Warming: Planetary heating rising well above 4C by 2100 could happen if climate action collapses or if strong feedback loops like the Amazon rainforest becoming a net carbon source emit its vast reserves of carbon. This would cause severe and lengthy heatwaves and water shortages affecting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the North Atlantic current, is weakening and showing signs of collapse due to global heating. A collapse commencing by 2030 would lead to a six-degree temperature drop in the UK. "Farming would face immense difficulties and water resources would be drastically changed," noted the professor.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in the polar regions collapse rapidly, inundating coastal cities and towns. In contrast to the other scenarios, this threat is already recognized by planners.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if industrial aerosols is drastically reduced. This paradoxical outcome occurs because tiny specks from industrial activity reflect solar radiation from warming the ground.

Building Resilience Against the Worst

These dire projections could be utilized in planning the construction of major projects, for example expanded cities, energy plants and urban drainage systems. Understanding these climate risks could also hasten the drive to cut fossil fuel emissions.

The analysis developed the extreme models using a blend of observed and historical experience, climate models and established principles. These outcomes do not take into account international cascading effects including the global food shortages and increased conflict.

This work was commissioned as part of a national risk assessment framework. Independent analyses have stated that not enough attention was being allocated to high-consequence, low-probability risks.

Official experts has said that the UK needs to "become resilient to moderate heating" and assess the risks for severe warming. Earlier government strategies have been criticised as being "inadequate" by certain experts.

A government spokesperson said: "Global warming is at the core of the country's focus, both building resilience and becoming a clean energy superpower. It is vital that the UK is resilient for the consequences."