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The direst possible consequences of the climate emergency for the UK have been mapped by experts, ranging from a scorching 4C rise in average temperatures to a two-metre surge in sea level. Another scenario predicts a decline of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would massively disrupt food production and power requirements.

Possible Events, Not Guarantees

These effects, a number of which are connected to critical climate thresholds, are considered as unlikely but credible. The team said that these projections plugged a hole in forecasting that had rendered the UK unprepared for catastrophic possibilities.

"The climate extremes we have outlined aren’t predictions, but they are credible," stated Nigel Arnell who led the analysis. "The nation has been planning in the absence of the tools to test against extreme possibilities. We've now supplied decision-makers what they need to plan for climate outcomes they hope never happen, but must not overlook."

A Range of Harsh Climate Projections

A further series of severe models maps the potential extent of harsh climate between now and the close of the 2100s. These suggest that temperatures could rocket in particular seasons by up to 6C above historical levels, while rainfall could be triple normal levels.

The likelihood of the extreme scenarios happening could not be calculated due to uncertainty about what steps will be taken to tackle climate change and how the planet's climate will respond. This research was compared to defence planning or resilience checks for financial systems.

Critical Scenario Highlights

• Severe Heating: Worldwide averages rising well above 4C by 2100 could happen if international cooperation breaks down or if strong feedback loops including the Amazon basin dying release its huge repository of carbon. This would lead to extreme and prolonged heatwaves and droughts plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is losing strength and losing stability due to ocean warming. A full shutdown commencing by 2030 would lead to a six-degree temperature drop in the UK. "Crop production would be severely challenged and water supplies would be drastically changed," noted the professor.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in Greenland and Antarctica collapse rapidly, submerging coastal cities and towns. Unlike the other scenarios, this risk is already understood by infrastructure experts.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if airborne particulates is drastically reduced. This paradoxical outcome occurs because tiny specks from fossil fuel combustion reflect sunlight from warming the ground.

Building Resilience Against the Unthinkable

These dire projections could be applied to guide the building of long-term infrastructure, for example housing developments, energy plants and water management networks. Knowledge about these environmental threats could also speed the transition to cut greenhouse gas emissions.

The analysis created the extreme models using a blend of observed and historical experience, digital projections and scientific theory. The scenarios exclude international cascading effects like the agricultural collapse and increased conflict.

The project was initiated as part of a official adaptation planning initiative. Previous assessments have stated that too little consideration was being allocated to catastrophic yet improbable risks.

Official experts has stated that the UK must "become resilient to moderate heating" and examine the threats for severe warming. Earlier government strategies have been criticised as being "inadequate" by environmental groups.

An official statement said: "Global warming is at the heart of the country's focus, both preparing for impacts and transitioning to a clean energy superpower. It is crucial that the UK is resilient for the effects."