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The gravest possible consequences of the global heating for the UK have been outlined by scientists, encompassing a blistering 4C increase in average temperatures to a two-metre increase in sea level. Another scenario predicts a decline of 6C in temperature following the collapse of crucial Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Credible Outcomes, Not Guarantees

These consequences, some of which are connected to critical climate thresholds, are viewed as low probability but plausible. The researchers stated that these scenarios plugged a hole in risk assessment that had rendered the UK not ready for extreme outcomes.

"The worst-case scenarios we have mapped aren’t predictions, but they are plausible," commented Nigel Arnell who led the research. "The nation has been making preparations in the absence of the tools to assess worst-case scenarios. We've now given policymakers what they need to plan for climate outcomes they wish to avoid, but dare not dismiss."

A Range of Extreme Weather Possibilities

A further series of dire projections maps the potential extent of extreme weather between now and the end of the century. These suggest that temperatures could soar in some months by up to 6C above average, while rainfall could be triple typical amounts.

The likelihood of the extreme scenarios coming to pass could not be calculated due to a lack of certainty about what measures will be implemented to combat climate change and how the planet's climate will react. This approach was compared to national security risk assessments or scenario planning for economic stability.

Key Possibility Details

• Four-Degree Warming: Global temperatures rising well above 4C by 2100 could happen if emissions cuts breaks down or if powerful amplifying effects including the tropical forests becoming a net carbon source release its vast reserves of carbon. This would result in extreme and prolonged heat domes and dry spells hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the North Atlantic current, is losing strength and becoming unstable due to global heating. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Crop production would face immense difficulties and water supplies would be fundamentally reshaped," noted the professor.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in the Arctic and Antarctic collapse rapidly, submerging seaside communities. Differing from the other scenarios, this threat is already understood by infrastructure experts.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because aerosol particles from industrial activity scatter sunlight from reaching the ground.

Building Resilience Against the Extreme

The severe models could be used to inform the building of critical national infrastructure, including new towns, energy plants and water management networks. Knowledge about these future hazards could also hasten the push to slash fossil fuel emissions.

The study created the worst-case scenarios using a mix of real-world events, computer simulations and climate physics. The scenarios do not take into account potential global problems like the agricultural collapse and resource wars.

The project was initiated as part of a official risk assessment framework. Earlier reports have warned that too little consideration was being allocated to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK must "prepare for two degrees of warming" and examine the risks for 4C. Earlier government strategies have been labeled being "inadequate" by environmental groups.

A national response noted: "Global warming is at the heart of the country's focus, both building resilience and establishing itself as a low-carbon economy. It is vital that the UK is resilient for the impacts."