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The most severe potential impacts of the climate emergency for the UK have been mapped by scientists, ranging from a blistering 4C increase in temperatures to a 2-metre surge in ocean levels. An alternative projection foresees a drop of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would massively disrupt farming and power requirements.

Plausible Extremes, Not Forecasts

These effects, certain ones are connected to critical climate thresholds, are seen as low probability but possible. The scientists said that these models filled a gap in planning that had rendered the UK ill-prepared for worst-case results.

"The worst-case scenarios we have mapped aren’t predictions, but they are plausible," commented Nigel Arnell who oversaw the analysis. "The UK has been formulating policy lacking the tools to plan for catastrophic outcomes. We've now provided planners what they need to prepare for environmental results they pray never occur, but dare not dismiss."

A Spectrum of Severe Conditions Projections

A further series of worst-case scenarios maps the projected severity of extreme weather between now and the end of the century. These show that temperatures could rocket in certain periods by up to 6C above the norm, while rainfall could be triple normal levels.

The chance of the worst-case outcomes happening cannot be precisely determined due to unknown factors about what steps will be enacted to address global warming and how the planet's climate will behave. This analysis was likened to national security risk assessments or resilience checks for financial systems.

Critical Scenario Details

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could occur if climate action collapses or if strong feedback loops like the Amazon rainforest becoming a net carbon source unleash its huge repository of carbon. This would lead to severe and lengthy heat domes and droughts affecting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is slowing down and showing signs of collapse due to global heating. A collapse starting around 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would face immense difficulties and water supplies would be completely altered," explained the lead researcher.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in Greenland and Antarctica melt abruptly, inundating seaside communities. In contrast to the other scenarios, this risk is already recognized by infrastructure experts.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if airborne particulates is sharply cut. This unexpected result occurs because tiny specks from industrial activity scatter sunlight from reaching the ground.

Preparing for the Worst

These dire projections could be utilized in planning the building of major projects, including new towns, energy plants and flood defences. Knowledge about these future hazards could also speed the drive to reduce fossil fuel emissions.

The study formulated the severe projections using a combination of real-world events, computer simulations and established principles. These outcomes do not take into account potential global problems including the devastation of food supplies and increased conflict.

The research was commissioned as part of a official risk assessment framework. Earlier reports have stated that insufficient focus was being allocated to low‐likelihood but high‐impact risks.

The government's climate advisors has stated that the UK must "become resilient to moderate heating" and assess the threats for severe warming. Past policy documents have been described as being "very weak" by some observers.

A government spokesperson commented: "The climate emergency is at the heart of the country's focus, both building resilience and becoming a clean energy superpower. It is essential that the UK is resilient for the consequences."