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The most severe possible consequences of the global heating for the UK have been mapped by experts, encompassing a blistering 4C jump in temperatures to a two-metre rise in sea level. An alternative projection envisions a drop of 6C in temperatures following the failure of key Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Extremes, Not Predictions

These effects, certain ones are linked to climate tipping points, are considered as unlikely but credible. The team stated that these projections plugged a hole in risk assessment that had left the UK not ready for worst-case results.

"The climate extremes we have mapped should not be seen as certainties, but they are possible," commented the professor who led the study. "The nation has been planning lacking the tools to assess catastrophic outcomes. We've now supplied policymakers what they need to plan for climate outcomes they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Possibilities

A second set of severe models sets out the potential extent of harsh climate between now and the end of the century. These suggest that thermometer readings could skyrocket in certain periods by up to 6C higher than historical levels, while precipitation could be 300% of normal levels.

The chance of the catastrophic events happening remains uncertain due to a lack of certainty about what measures will be taken to address global heating and how the planet's climate will behave. This approach was compared to national security risk assessments or scenario planning for the banking sector.

Major Outcome Details

• 4C Temperature Rise: Planetary heating rising well above 4C by 2100 could happen if international cooperation collapses or if powerful amplifying effects including the Amazon rainforest becoming a net carbon source unleash its vast reserves of carbon. This would result in extreme and prolonged heat domes and droughts hitting the UK in summer.
• Ocean Circulation Failure: A major ocean current, the AMOC, is losing strength and showing signs of collapse due to ocean warming. A complete failure commencing by 2030 would lead to a 6C cooling in the UK. "Crop production would struggle enormously and water supplies would be completely altered," explained Arnell.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the polar regions disintegrate quickly, inundating seaside communities. Differing from the other scenarios, this risk is already recognized by planners.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because pollution particles from industrial activity scatter solar radiation from reaching the ground.

Preparing for the Extreme

The severe models could be utilized in planning the development of long-term infrastructure, such as expanded cities, power generation facilities and water management networks. Knowledge about these climate risks could also accelerate the transition to cut carbon pollution.

The analysis developed the worst-case scenarios using a blend of past data and records, climate models and established principles. These outcomes exclude potential global problems including the devastation of food supplies and resource wars.

The research was commissioned as part of a government’s climate resilience programme. Independent analyses have stated that too little consideration was being given to high-consequence, low-probability risks.

An independent advisory body has recommended that the UK must "prepare for two degrees of warming" and evaluate the risks for severe warming. Past policy documents have been labeled being "insufficient" by certain experts.

An official statement said: "Climate change is at the center of our national priorities, both adapting for the future and establishing itself as a low-carbon economy. It is vital that the UK is resilient for the effects."