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The gravest projected effects of the climate emergency for the UK have been detailed by scientists, encompassing a scorching 4C rise in average temperatures to a 2-metre increase in sea levels. An alternative projection envisions a drop of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would severely impact farming and energy demand.

Credible Extremes, Not Predictions

These consequences, certain ones are linked to climate tipping points, are seen as low probability but plausible. The researchers stated that these scenarios filled a gap in risk assessment that had left the UK unprepared for worst-case results.

"The severe weather events we have detailed aren’t predictions, but they are credible," commented the lead researcher who oversaw the study. "The nation has been formulating policy without the frameworks to test against extreme possibilities. We've now provided policymakers what they need to get ready for environmental results they pray never occur, but can’t afford to ignore."

A Range of Severe Conditions Scenarios

Another collection of worst-case scenarios sets out the potential extent of extreme weather between now and the close of the 2100s. These indicate that thermometer readings could soar in certain periods by up to 6C above historical levels, while rainfall could be triple normal levels.

The likelihood of the worst-case outcomes occurring could not be calculated due to uncertainty about what action will be taken to address global warming 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 Elements

• 4C Temperature Rise: Planetary heating soaring past 4C by 2100 could happen if climate action breaks down or if powerful amplifying effects such as the tropical forests becoming a net carbon source emit its huge repository of carbon. This would cause intense and enduring heatwaves and droughts hitting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the AMOC, is weakening and becoming unstable due to global heating. A full shutdown starting around 2030 would lead to a 6C cooling in the UK. "Crop production would struggle enormously and water resources would be completely altered," said the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in Greenland and Antarctica melt abruptly, submerging low-lying areas. Unlike the other scenarios, this risk is already known by coastal engineers.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This paradoxical outcome occurs because pollution particles from burning coal scatter sunlight from reaching the ground.

Planning for the Extreme

The worst-case scenarios could be applied to guide the construction of major projects, for example housing developments, energy plants and water management networks. Knowledge about these environmental threats could also speed the push to slash fossil fuel emissions.

The research developed the worst-case scenarios using a blend of observed and historical experience, climate models and established principles. These outcomes do not take into account potential global problems like the global food shortages and increased conflict.

The project was requested as part of a government’s adaptation planning initiative. Earlier reports have warned that insufficient focus was being allocated to catastrophic yet improbable risks.

An independent advisory body has stated that the UK must "adapt to 2C" and examine the threats for 4C. Earlier government strategies have been criticised as being "insufficient" by some observers.

A national response noted: "The climate emergency is at the heart of the country's focus, both building resilience and transitioning to a renewable energy leader. It is essential that the UK is resilient for the impacts."