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The direst projected effects of the global heating for the UK have been detailed by scientists, ranging from a searing 4C rise in average temperatures to a 2-metre increase in ocean levels. Another scenario foresees a decline of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset agriculture and energy demand.

Plausible Outcomes, Not Guarantees

These impacts, a number of which are linked to critical climate thresholds, are viewed as low probability but possible. The researchers said that these projections addressed a shortfall in forecasting that had rendered the UK not ready for worst-case results.

"The climate extremes we have outlined are not forecasts, but they are possible," stated Nigel Arnell who directed the research. "The UK has been planning without the tools to test against catastrophic outcomes. We've now supplied planners what they need to plan for climate outcomes they pray never occur, but must not overlook."

A Spectrum of Harsh Climate Possibilities

Another collection of dire projections maps the possible scale of extreme weather between now and the end of the century. These show that thermometer readings could soar in particular seasons by up to 6C above historical levels, while rainfall could be triple typical amounts.

The likelihood of the catastrophic events happening cannot be precisely determined due to unknown factors about what steps will be implemented to combat climate change and how the Earth's systems will react. This research was likened to security threat evaluations or scenario planning for financial systems.

Major Scenario Elements

• Severe Heating: Worldwide averages rising well above 4C by 2100 could transpire if emissions cuts collapses or if strong feedback loops like the Amazon basin becoming a net carbon source release its vast reserves of carbon. This would result in extreme and prolonged heat domes and water shortages affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is losing strength and losing stability due to climate change. A full shutdown beginning in 2030 would lead to a 6C cooling in the UK. "Agriculture would face immense difficulties and freshwater availability would be completely altered," noted the professor.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica disintegrate quickly, inundating seaside communities. Differing from the other scenarios, this possibility is already understood by coastal engineers.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if pollution from industry is rapidly cleaned up. This unexpected result occurs because aerosol particles from fossil fuel combustion scatter sunlight from reaching the ground.

Planning for the Worst

The worst-case scenarios could be used to inform the building of critical national infrastructure, such as new towns, power generation facilities and water management networks. Knowledge about these climate risks could also speed the drive to reduce fossil fuel emissions.

The study created the severe projections using a combination of real-world events, climate models and established principles. These outcomes exclude potential global problems like the agricultural collapse and geopolitical instability.

The research was initiated as part of a government’s adaptation planning initiative. Earlier reports have stated that not enough attention was being given to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK must "become resilient to moderate heating" and evaluate the threats for 4C. Earlier government strategies have been criticised as being "inadequate" by certain experts.

A national response commented: "The climate emergency is at the center of our national priorities, both adapting for the future and establishing itself as a clean energy superpower. It is crucial that the UK is resilient for the effects."