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The gravest projected effects of the climate emergency for the UK have been mapped by researchers, ranging from a blistering 4C jump in average temperatures to a 6.5-foot surge in sea level. An alternative projection envisions a decline of 6C in temperature following the collapse of critical Atlantic Ocean currents, which would massively disrupt food production and energy demand.

Credible Outcomes, Not Forecasts

These impacts, some of which are associated with climate tipping points, are seen as improbable but plausible. The scientists stated that these models filled a gap in risk assessment that had left the UK not ready for catastrophic possibilities.

"The severe weather events we have detailed are not forecasts, but they are credible," commented the lead researcher who directed the analysis. "The nation has been making preparations lacking the tools to assess catastrophic outcomes. We've now given planners what they need to plan for climate outcomes they pray never occur, but must not overlook."

A Spectrum of Harsh Climate Scenarios

A second set of severe models maps the possible scale of harsh climate between now and the year 2100. These indicate that thermometer readings could rocket in particular seasons by up to 6C above average, while precipitation could be triple typical amounts.

The probability of the worst-case outcomes occurring could not be calculated due to uncertainty about what action will be implemented to address global heating and how the Earth's systems will react. This research was likened to defence planning or stress tests for economic stability.

Critical Scenario Highlights

• Four-Degree Warming: Worldwide averages soaring past 4C by 2100 could occur if international cooperation fails or if vicious cycles including the tropical forests becoming a net carbon source release its huge repository of carbon. This would cause extreme and prolonged heatwaves and droughts plaguing the UK in summer.
• Ocean Circulation Failure: A major ocean current, the North Atlantic current, is slowing down and losing stability due to ocean warming. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would face immense difficulties and water supplies would be drastically changed," explained the professor.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in Greenland and Antarctica disintegrate quickly, submerging low-lying areas. Differing from the other scenarios, this risk is already known by planners.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if industrial aerosols is rapidly cleaned up. This unexpected result occurs because tiny specks from burning coal block solar radiation from reaching the ground.

Planning for the Unthinkable

These dire projections could be applied to guide the construction of major projects, including new towns, nuclear power stations and water management networks. Understanding these future hazards could also hasten the drive to cut fossil fuel emissions.

The analysis formulated the extreme models using a mix of real-world events, climate models and established principles. The scenarios exclude international cascading effects such as the devastation of food supplies and resource wars.

This work was initiated as part of a national risk assessment framework. Previous assessments have cautioned that too little consideration was being given to high-consequence, low-probability risks.

An independent advisory body has recommended that the UK must "prepare for two degrees of warming" and assess the threats for four degrees. Past policy documents have been criticised as being "insufficient" by environmental groups.

An official statement said: "The climate emergency is at the center of the country's focus, both building resilience and becoming a clean energy superpower. It is vital that the UK is prepared for the impacts."