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The direst potential impacts of the climate emergency for the UK have been outlined by researchers, encompassing a scorching 4C increase in average temperatures to a two-metre surge in sea level. Another scenario envisions a decline of 6C in temperature following the collapse of key Atlantic Ocean currents, which would massively disrupt food production and energy needs.

Credible Outcomes, Not Predictions

These effects, a number of which are associated with critical climate thresholds, are viewed as improbable but plausible. The researchers explained that these scenarios plugged a hole in risk assessment that had rendered the UK not ready for worst-case results.

"The climate extremes we have mapped should not be seen as certainties, but they are credible," stated the professor who oversaw the research. "The UK has been planning without the frameworks to plan for worst-case scenarios. We've now provided decision-makers what they need to plan for environmental results they hope never happen, but can’t afford to ignore."

A Suite of Harsh Climate Scenarios

A second set of severe models details the projected severity of harsh climate between now and the end of the century. These indicate that thermometer readings could soar in some months by up to 6C above historical levels, while rainfall could be 300% of standard measurements.

The likelihood of the worst-case outcomes happening could not be calculated due to uncertainty about what action will be enacted to combat climate change and how the climate system will react. This analysis was described as similar to national security risk assessments or resilience checks for economic stability.

Critical Outcome Elements

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could occur if climate action breaks down or if strong feedback loops including the tropical forests perishing emit its enormous store of carbon. This would lead to extreme and prolonged heatwaves and dry spells affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the North Atlantic current, is losing strength and losing stability due to climate change. A complete failure starting around 2030 would lead to a six-degree temperature drop in the UK. "Crop production would be severely challenged and water resources would be drastically changed," said Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica melt abruptly, flooding low-lying areas. Unlike the other scenarios, this threat is already recognized by coastal engineers.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if industrial aerosols is rapidly cleaned up. This counterintuitive effect occurs because aerosol particles from industrial activity scatter solar radiation from warming the ground.

Building Resilience Against the Worst

The worst-case scenarios could be used to inform the construction of critical national infrastructure, including new towns, power generation facilities and urban drainage systems. Awareness of these climate risks could also speed the transition to reduce greenhouse gas emissions.

The analysis created the extreme models using a mix of real-world events, climate models and climate physics. These outcomes do not take into account international cascading effects like the agricultural collapse and geopolitical instability.

The project was commissioned as part of a national risk assessment framework. Independent analyses have stated that too little consideration was being allocated to catastrophic yet improbable risks.

An independent advisory body has said that the UK must "adapt to 2C" and evaluate the threats for severe warming. Previous adaptation plans have been criticised as being "insufficient" by certain experts.

A government spokesperson said: "Climate change is at the heart of this government’s agenda, both adapting for the future and establishing itself as a low-carbon economy. It is vital that the UK is resilient for the effects."