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The direst projected effects of the global heating for the UK have been mapped by experts, ranging from a searing 4C jump in mean temperatures to a 6.5-foot rise in ocean levels. An alternative projection envisions a decline of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would severely impact farming and energy demand.

Plausible Events, Not Predictions

These effects, a number of which are associated with climate tipping points, are viewed as unlikely but possible. The team explained that these projections filled a gap in forecasting that had left the UK not ready for catastrophic possibilities.

"The worst-case scenarios we have mapped aren’t predictions, but they are credible," said the professor who directed the analysis. "Britain has been formulating policy lacking the frameworks to test against extreme possibilities. We've now provided planners what they need to plan for climate outcomes they hope never happen, but must not overlook."

A Suite of Harsh Climate Projections

A further series of worst-case scenarios details the projected severity of extreme weather between now and the year 2100. These indicate that thermometer readings could skyrocket in particular seasons by up to 6C above average, while rainfall could be 300% of typical amounts.

The likelihood of the worst-case outcomes happening cannot be precisely determined due to uncertainty about what measures will be implemented to combat climate change and how the climate system will react. This research was compared to national security risk assessments or stress tests for financial systems.

Key Scenario Highlights

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could transpire if international cooperation breaks down or if vicious cycles like the Amazon rainforest dying release its vast reserves of carbon. This would lead to intense and enduring heatwaves and dry spells affecting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is slowing down and becoming unstable due to climate change. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and water supplies would be drastically changed," explained the lead researcher.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic collapse rapidly, submerging seaside communities. Differing from the other scenarios, this possibility is already known by coastal engineers.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because pollution particles from industrial activity reflect solar radiation from reaching the ground.

Preparing for the Extreme

The worst-case scenarios could be applied to guide the development of long-term infrastructure, such as housing developments, power generation facilities and urban drainage systems. Understanding these future hazards could also accelerate the push to reduce greenhouse gas emissions.

The research formulated the extreme models using a combination of past data and records, digital projections and scientific theory. These outcomes omit international cascading effects like the agricultural collapse and geopolitical instability.

The research was initiated as part of a official risk assessment framework. Independent analyses have warned that not enough attention was being paid to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "prepare for two degrees of warming" and evaluate the dangers for severe warming. Previous adaptation plans have been labeled being "insufficient" by certain experts.

A government spokesperson said: "Climate change is at the heart of our national priorities, both adapting for the future and transitioning to a low-carbon economy. It is crucial that the UK is resilient for the impacts."