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The gravest potential impacts of the climate crisis for the UK have been detailed by researchers, including a searing 4C jump in temperatures to a 6.5-foot rise in sea levels. A separate possibility foresees a plunge of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would massively disrupt food production and energy demand.

Plausible Extremes, Not Guarantees

These impacts, a number of which are associated with critical climate thresholds, are seen as improbable but possible. The researchers stated that these scenarios filled a gap in planning that had left the UK unprepared for catastrophic possibilities.

"The worst-case scenarios we have outlined are not forecasts, but they are possible," said the lead researcher who oversaw the research. "The nation has been planning in the absence of the methods to assess catastrophic outcomes. We've now supplied decision-makers what they need to prepare for future conditions they wish to avoid, but dare not dismiss."

A Spectrum of Extreme Weather Scenarios

Another collection of worst-case scenarios sets out the possible scale of extreme weather between now and the close of the 2100s. These show that thermometer readings could rocket in particular seasons by up to 6C above the norm, while rainfall could be triple standard measurements.

The probability of the catastrophic events occurring remains uncertain due to a lack of certainty about what measures will be enacted to combat global heating and how the planet's climate will behave. This analysis was compared to national security risk assessments or stress tests for financial systems.

Key Scenario Details

• Severe Heating: Planetary heating exceeding 4C by 2100 could occur if international cooperation collapses or if powerful amplifying effects such as the Amazon rainforest becoming a net carbon source release its vast reserves of carbon. This would cause intense and enduring heatwaves and droughts plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is losing strength and showing signs of collapse due to climate change. A full shutdown beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and water resources would be fundamentally reshaped," explained the lead researcher.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the Arctic and Antarctic melt abruptly, flooding low-lying areas. In contrast to the other scenarios, this threat is already understood by coastal engineers.
• Aerosol Effect: Global averages could also be increased by about 0.75C if industrial aerosols is sharply cut. This paradoxical outcome occurs because pollution particles from industrial activity block sunlight from warming the ground.

Building Resilience Against the Worst

The severe models could be used to inform the development of critical national infrastructure, including expanded cities, power generation facilities and urban drainage systems. Awareness of these future hazards could also accelerate the drive to reduce greenhouse gas emissions.

The research created the severe projections using a mix of observed and historical experience, digital projections and scientific theory. The possibilities omit potential global problems like the devastation of food supplies and geopolitical instability.

This work was initiated as part of a national adaptation planning initiative. Previous assessments have warned that not enough attention was being given to high-consequence, low-probability risks.

The government's climate advisors has recommended that the UK must "prepare for two degrees of warming" and evaluate the risks for severe warming. Past policy documents have been labeled being "inadequate" by certain experts.

A government spokesperson commented: "Climate change is at the center of this government’s agenda, both preparing for impacts and transitioning to a low-carbon economy. It is crucial that the UK is resilient for the impacts."