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The direst possible consequences of the climate crisis for the UK have been detailed by researchers, encompassing a blistering 4C rise in mean temperatures to a two-metre surge in sea levels. An alternative projection envisions a plunge of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would profoundly upset agriculture and power requirements.

Credible Extremes, Not Guarantees

These effects, a number of which are associated with climate tipping points, are viewed as low probability but possible. The team explained that these projections plugged a hole in planning that had rendered the UK not ready for extreme outcomes.

"The climate extremes we have mapped aren’t predictions, but they are possible," stated the lead researcher who led the analysis. "Britain has been planning without the methods to plan for catastrophic outcomes. We've now supplied policymakers what they need to plan for environmental results they hope never happen, but can’t afford to ignore."

A Suite of Extreme Weather Projections

A further series of severe models maps the potential extent of severe conditions between now and the year 2100. These indicate that temperatures could skyrocket in certain periods by up to 6C above average, while rainfall could be triple standard measurements.

The chance of the catastrophic events happening cannot be precisely determined due to a lack of certainty about what action will be implemented to tackle global warming and how the planet's climate will respond. This approach was described as similar to national security risk assessments or stress tests for economic stability.

Critical Outcome Elements

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could occur if emissions cuts fails or if vicious cycles like the Amazon basin perishing release its huge repository of carbon. This would result in intense and enduring heat domes and dry spells plaguing the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is losing strength and showing signs of collapse due to climate change. A collapse starting around 2030 would lead to a drastic cooling in the UK. "Crop production would struggle enormously and freshwater availability would be completely altered," noted the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica disintegrate quickly, flooding seaside communities. In contrast to the other scenarios, this possibility is already known by coastal engineers.
• Aerosol Effect: Temperatures could also be pushed higher by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from fossil fuel combustion reflect sunlight from reaching the ground.

Preparing for the Extreme

The severe models could be used to inform the construction of major projects, such as expanded cities, nuclear power stations and water management networks. Awareness of these environmental threats could also speed the push to cut greenhouse gas emissions.

The study developed the worst-case scenarios using a blend of past data and records, computer simulations and scientific theory. The scenarios omit international cascading effects like the global food shortages and increased conflict.

The project was requested as part of a government’s adaptation planning initiative. Previous assessments have cautioned that too little consideration was being allocated to high-consequence, low-probability risks.

An independent advisory body has said that the UK needs to "become resilient to moderate heating" and assess the risks for four degrees. Earlier government strategies have been labeled being "insufficient" by some observers.

A government spokesperson commented: "Climate change is at the center of our national priorities, both preparing for impacts and transitioning to a renewable energy leader. It is crucial that the UK is ready for the impacts."