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The direst projected effects of the global heating for the UK have been detailed by scientists, including a blistering 4C jump in average temperatures to a 2-metre surge in ocean levels. Another scenario foresees a plunge of 6C in temperatures following the failure of crucial Atlantic Ocean currents, which would profoundly upset agriculture and energy needs.

Possible Events, Not Guarantees

These consequences, some of which are connected to irreversible climate shifts, are seen as low probability but credible. The team explained that these projections plugged a hole in planning that had rendered the UK ill-prepared for extreme outcomes.

"The severe weather events we have detailed aren’t predictions, but they are credible," stated Nigel Arnell who oversaw the research. "Britain has been formulating policy lacking the tools to plan for worst-case scenarios. We've now given planners what they need to prepare for future conditions they hope never happen, but can’t afford to ignore."

A Suite of Severe Conditions Scenarios

A second set of dire projections maps the possible scale of harsh climate between now and the close of the 2100s. These indicate that thermometer readings could rocket in particular seasons by up to 6C higher than the norm, while precipitation could be three times standard measurements.

The chance of the extreme scenarios coming to pass remains uncertain due to a lack of certainty about what action will be taken to combat global warming and how the planet's climate will behave. This analysis was likened to security threat evaluations or stress tests for financial systems.

Key Scenario Details

• 4C Temperature Rise: Worldwide averages exceeding 4C by 2100 could happen if climate action collapses or if vicious cycles such as the tropical forests dying unleash its huge repository of carbon. This would cause extreme and prolonged heat domes and water shortages affecting the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is weakening and showing signs of collapse due to global heating. A collapse commencing by 2030 would lead to a drastic cooling in the UK. "Farming would be severely challenged and freshwater availability would be fundamentally reshaped," noted the lead researcher.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the Arctic and Antarctic disintegrate quickly, submerging seaside communities. Unlike the other scenarios, this possibility is already known by planners.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if industrial aerosols is rapidly cleaned up. This counterintuitive effect occurs because aerosol particles from industrial activity block solar radiation from reaching the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be applied to guide the building of critical national infrastructure, for example new towns, power generation facilities and water management networks. Knowledge about these climate risks could also hasten the drive to reduce greenhouse gas emissions.

The research developed the severe projections using a blend of past data and records, computer simulations and climate physics. These outcomes exclude potential global problems such as the global food shortages and increased conflict.

The research was requested as part of a official adaptation planning initiative. Previous assessments have cautioned that insufficient focus was being paid to high-consequence, low-probability risks.

The government's climate advisors has recommended that the UK must "prepare for two degrees of warming" and examine the risks for four degrees. Past policy documents have been labeled being "inadequate" by environmental groups.

An official statement commented: "Global warming is at the center of our national priorities, both preparing for impacts and becoming a renewable energy leader. It is essential that the UK is prepared for the consequences."