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The gravest projected effects of the climate emergency for the UK have been detailed by experts, encompassing a scorching 4C increase in temperatures to a 2-metre increase in ocean levels. An alternative projection predicts a drop of 6C in temperature following the collapse of crucial Atlantic Ocean currents, which would profoundly upset agriculture and energy demand.

Plausible Extremes, Not Guarantees

These consequences, a number of which are linked to critical climate thresholds, are seen as unlikely but credible. The researchers said that these scenarios addressed a shortfall in risk assessment that had left the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined aren’t predictions, but they are possible," stated the professor who directed the study. "The nation has been making preparations lacking the frameworks to test against extreme possibilities. We've now supplied policymakers what they need to prepare for climate outcomes they hope never happen, but can’t afford to ignore."

A Suite of Severe Conditions Scenarios

A second set of dire projections details the projected severity of severe conditions between now and the year 2100. These suggest that temperatures could skyrocket in some months by up to 6C above historical levels, while precipitation could be 300% of typical amounts.

The likelihood of the catastrophic events happening cannot be precisely determined due to unknown factors about what action will be enacted to address climate change and how the planet's climate will respond. This research was described as similar to defence planning or stress tests for the banking sector.

Critical Outcome Highlights

• Severe Heating: Global temperatures exceeding 4C by 2100 could happen if international cooperation breaks down or if powerful amplifying effects such as the Amazon basin becoming a net carbon source release its enormous store of carbon. This would cause intense and enduring heat domes and droughts affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the AMOC, is slowing down and losing stability due to ocean warming. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Agriculture would be severely challenged and water supplies would be drastically changed," explained the professor.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the Arctic and Antarctic melt abruptly, flooding seaside communities. Unlike the other scenarios, this threat is already understood by coastal engineers.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because tiny specks from burning coal block solar radiation from warming the ground.

Preparing for the Worst

The severe models could be used to inform the building of critical national infrastructure, including housing developments, energy plants and water management networks. Awareness of these environmental threats could also hasten the push to slash carbon pollution.

The research created the severe projections using a blend of observed and historical experience, digital projections and established principles. The scenarios omit broader worldwide issues such as the agricultural collapse and increased conflict.

The project was requested as part of a national climate resilience programme. Previous assessments have cautioned that too little consideration was being given to low‐likelihood but high‐impact risks.

Official experts has recommended that the UK needs to "prepare for two degrees of warming" and assess the threats for severe warming. Earlier government strategies have been criticised as being "insufficient" by some observers.

A government spokesperson commented: "Global warming is at the core of this government’s agenda, both building resilience and transitioning to a renewable energy leader. It is vital that the UK is ready for the consequences."