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The most severe projected effects of the climate emergency for the UK have been outlined by scientists, encompassing a searing 4C increase in mean temperatures to a two-metre increase in ocean levels. A separate possibility predicts a plunge of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would massively disrupt food production and energy needs.

Possible Events, Not Guarantees

These consequences, some of which are connected to critical climate thresholds, are viewed as improbable but plausible. The researchers explained that these projections plugged a hole in risk assessment that had left the UK not ready for catastrophic possibilities.

"The climate extremes we have outlined aren’t predictions, but they are credible," said Nigel Arnell who oversaw the research. "The nation has been planning lacking the frameworks to test against worst-case scenarios. We've now supplied planners what they need to plan for environmental results they wish to avoid, but dare not dismiss."

A Range of Harsh Climate Possibilities

A further series of dire projections maps the potential extent of extreme weather between now and the close of the 2100s. These indicate that thermometer readings could rocket in certain periods by up to 6C above average, while rainfall could be 300% of standard measurements.

The probability of the extreme scenarios occurring remains uncertain due to uncertainty about what measures will be implemented to tackle global heating and how the planet's climate will react. This analysis was described as similar to national security risk assessments or stress tests for the banking sector.

Major Outcome Highlights

• Severe Heating: Global temperatures rising well above 4C by 2100 could transpire if international cooperation fails or if powerful amplifying effects like the Amazon rainforest becoming a net carbon source unleash its huge repository of carbon. This would lead to intense and enduring heatwaves and droughts affecting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is losing strength and becoming unstable due to global heating. A full shutdown commencing by 2030 would lead to a six-degree temperature drop in the UK. "Crop production would struggle enormously and water supplies would be completely altered," explained Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic melt abruptly, inundating seaside communities. In contrast to the other scenarios, this possibility is already known by infrastructure experts.
• Clean Air Warming: Global averages could also be pushed higher by about 0.75C if industrial aerosols is sharply cut. This unexpected result occurs because aerosol particles from burning coal block solar radiation from warming the ground.

Preparing for the Worst

The worst-case scenarios could be used to inform the development of long-term infrastructure, for example new towns, power generation facilities and flood defences. Awareness of these future hazards could also accelerate the drive to cut carbon pollution.

The study developed the extreme models using a combination of past data and records, climate models and established principles. The scenarios do not take into account broader worldwide issues like the devastation of food supplies and geopolitical instability.

The research was requested as part of a government’s climate resilience programme. Independent analyses have warned that not enough attention was being allocated to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK needs to "prepare for two degrees of warming" and evaluate the threats for 4C. Past policy documents have been criticised as being "insufficient" by some observers.

A national response said: "Climate change is at the heart of this government’s agenda, both adapting for the future and transitioning to a low-carbon economy. It is essential that the UK is ready for the effects."