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The most severe possible consequences of the climate emergency for the UK have been detailed by scientists, including a searing 4C jump in average temperatures to a 2-metre increase in sea level. Another scenario envisions a drop of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would severely impact agriculture and power requirements.

Possible Outcomes, Not Forecasts

These impacts, certain ones are linked to climate tipping points, are seen as unlikely but credible. The team said that these projections filled a gap in forecasting that had left the UK not ready for extreme outcomes.

"The climate extremes we have detailed aren’t predictions, but they are credible," commented Nigel Arnell who led the analysis. "Britain has been making preparations without the frameworks to plan for worst-case scenarios. We've now provided policymakers what they need to get ready for future conditions they hope never happen, but can’t afford to ignore."

A Suite of Extreme Weather Possibilities

A further series of severe models sets out the projected severity of severe conditions between now and the end of the century. These suggest that thermometer readings could skyrocket in certain periods by up to 6C above average, while rainfall could be three times typical amounts.

The chance of the worst-case outcomes coming to pass cannot be precisely determined due to uncertainty about what action will be taken to combat global heating and how the planet's climate will react. This research was likened to national security risk assessments or stress tests for economic stability.

Critical Possibility Elements

• Four-Degree Warming: Planetary heating soaring past 4C by 2100 could transpire if international cooperation breaks down or if powerful amplifying effects such as the Amazon basin perishing emit its enormous store of carbon. This would lead to extreme and prolonged heat domes and droughts hitting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the North Atlantic current, is weakening and becoming unstable due to climate change. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Crop production would be severely challenged and water resources would be fundamentally reshaped," said the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the Arctic and Antarctic collapse rapidly, submerging seaside communities. In contrast to the other scenarios, this possibility is already understood by coastal engineers.
• Aerosol Effect: Global averages could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because aerosol particles from burning coal scatter solar radiation from warming the ground.

Building Resilience Against the Extreme

The severe models could be utilized in planning the development of critical national infrastructure, including housing developments, power generation facilities and water management networks. Understanding these future hazards could also hasten the transition to cut carbon pollution.

The research formulated the worst-case scenarios using a combination of observed and historical experience, climate models and established principles. The scenarios exclude potential global problems such as the devastation of food supplies and resource wars.

This work was commissioned as part of a national climate resilience programme. Earlier reports have warned that not enough attention was being given to low‐likelihood but high‐impact risks.

An independent advisory body has stated that the UK needs to "prepare for two degrees of warming" and assess the threats for four degrees. Past policy documents have been criticised as being "insufficient" by certain experts.

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