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The gravest potential impacts of the climate emergency for the UK have been mapped by researchers, encompassing a scorching 4C rise in temperatures to a 2-metre rise in sea levels. A separate possibility envisions a decline of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would massively disrupt food production and energy demand.

Plausible Outcomes, Not Forecasts

These consequences, a number of which are connected to climate tipping points, are seen as unlikely but plausible. The scientists stated that these models filled a gap in planning that had rendered the UK ill-prepared for catastrophic possibilities.

"The worst-case scenarios we have detailed are not forecasts, but they are possible," said Nigel Arnell who oversaw the analysis. "Britain has been planning lacking the tools to plan for extreme possibilities. We've now given decision-makers what they need to prepare for environmental results they wish to avoid, but must not overlook."

A Suite of Harsh Climate Projections

A further series of worst-case scenarios details the possible scale of severe conditions between now and the close of the 2100s. These suggest that temperatures could soar in certain periods by up to 6C above the norm, while rainfall could be three times normal levels.

The likelihood of the extreme scenarios happening could not be calculated due to unknown factors about what measures will be taken to address climate change and how the Earth's systems will react. This analysis was likened to national security risk assessments or stress tests for economic stability.

Key Outcome Details

• Severe Heating: Worldwide averages 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 unleash its vast reserves of carbon. This would cause extreme and prolonged heat domes and droughts hitting the UK in summer.
• AMOC Shutdown: A major ocean current, the AMOC, is losing strength and becoming unstable due to climate change. A collapse commencing by 2030 would lead to a 6C cooling in the UK. "Farming would struggle enormously and water resources would be drastically changed," explained Arnell.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in Greenland and Antarctica collapse rapidly, submerging coastal cities and towns. Differing from the other scenarios, this risk is already known by infrastructure experts.
• Aerosol Effect: Global averages could also be increased by about 0.75C if pollution from industry is rapidly cleaned up. This unexpected result occurs because pollution particles from burning coal reflect solar radiation from warming the ground.

Building Resilience Against the Worst

The severe models could be used to inform the development of long-term infrastructure, for example housing developments, power generation facilities and water management networks. Awareness of these future hazards could also speed the push to cut carbon pollution.

The study formulated the severe projections using a mix of past data and records, digital projections and climate physics. The possibilities do not take into account potential global problems like the global food shortages and resource wars.

The project was commissioned as part of a government’s adaptation planning initiative. Previous assessments have cautioned that insufficient focus was being allocated to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK must "prepare for two degrees of warming" and examine the threats for four degrees. Past policy documents have been labeled being "insufficient" by environmental groups.

An official statement commented: "Global warming is at the core of the country's focus, both building resilience and establishing itself as a low-carbon economy. It is vital that the UK is prepared for the impacts."