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The most severe projected effects of the climate crisis for the UK have been outlined by scientists, encompassing a searing 4C rise in average temperatures to a 2-metre increase in sea level. Another scenario predicts a decline of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would massively disrupt food production and energy needs.

Possible Events, Not Guarantees

These consequences, some of which are linked to climate tipping points, are viewed as low probability but plausible. The researchers explained that these models addressed a shortfall in risk assessment that had left the UK unprepared for worst-case results.

"The severe weather events we have mapped aren’t predictions, but they are credible," stated Nigel Arnell who directed the analysis. "Britain has been planning without the methods to plan for extreme possibilities. We've now supplied policymakers what they need to prepare for climate outcomes they wish to avoid, but can’t afford to ignore."

A Spectrum of Extreme Weather Possibilities

A second set of severe models details the possible scale of extreme weather between now and the year 2100. These show that thermometer readings could skyrocket in particular seasons by up to 6C higher than average, while rainfall could be three times standard measurements.

The chance of the extreme scenarios happening could not be calculated due to unknown factors about what steps will be taken to address climate change and how the planet's climate will respond. This approach was likened to security threat evaluations or scenario planning for economic stability.

Major Possibility Details

• Four-Degree Warming: Worldwide averages soaring past 4C by 2100 could transpire if climate action collapses or if powerful amplifying effects like the Amazon rainforest becoming a net carbon source emit its enormous store of carbon. This would lead to severe and lengthy heatwaves and water shortages affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and becoming unstable due to climate change. A full shutdown beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and water resources would be fundamentally reshaped," noted Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica melt abruptly, flooding low-lying areas. In contrast to the other scenarios, this threat is already recognized by coastal engineers.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if airborne particulates is rapidly cleaned up. This counterintuitive effect occurs because pollution particles from fossil fuel combustion block sunlight from warming the ground.

Building Resilience Against the Unthinkable

The severe models could be utilized in planning the building of long-term infrastructure, for example expanded cities, energy plants and flood defences. Knowledge about these climate risks could also speed the transition to cut carbon pollution.

The study created the severe projections using a mix of real-world events, digital projections and climate physics. The scenarios omit broader worldwide issues including the agricultural collapse and increased conflict.

The research was initiated as part of a government’s adaptation planning initiative. Independent analyses have stated that insufficient focus was being given to high-consequence, low-probability risks.

The government's climate advisors has said that the UK must "become resilient to moderate heating" and evaluate the threats for four degrees. Earlier government strategies have been described as being "inadequate" by some observers.

A government spokesperson said: "Climate change is at the heart of our national priorities, both building resilience and transitioning to a low-carbon economy. It is essential that the UK is resilient for the impacts."