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The direst possible consequences of the climate emergency for the UK have been outlined by experts, ranging from a scorching 4C increase in mean temperatures to a two-metre surge in sea level. Another scenario predicts a decline of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would profoundly upset agriculture and power requirements.

Credible Outcomes, Not Guarantees

These consequences, a number of which are connected to climate tipping points, are seen as unlikely but credible. The team stated that these projections filled a gap in planning that had left the UK ill-prepared for worst-case results.

"The climate extremes we have detailed aren’t predictions, but they are plausible," said the professor who led the analysis. "Britain has been planning without the tools to test against catastrophic outcomes. We've now supplied policymakers what they need to plan for future conditions they pray never occur, but must not overlook."

A Suite of Severe Conditions Projections

Another collection of severe models details the potential extent of harsh climate between now and the end of the century. These suggest that temperatures could skyrocket in some months by up to 6C higher than historical levels, while precipitation could be three times normal levels.

The chance of the catastrophic events coming to pass could not be calculated due to a lack of certainty about what steps will be enacted to tackle global warming and how the Earth's systems will behave. This research was compared to security threat evaluations or resilience checks for economic stability.

Key Possibility Elements

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could transpire if international cooperation collapses or if strong feedback loops including the Amazon rainforest dying unleash its enormous store of carbon. This would lead to intense and enduring heat domes and water shortages hitting the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is slowing down and losing stability due to global heating. A full shutdown starting around 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and water supplies would be fundamentally reshaped," noted the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the Arctic and Antarctic disintegrate quickly, flooding coastal cities and towns. In contrast to the other scenarios, this threat is already understood by infrastructure experts.
• Clean Air Warming: Temperatures could also be increased by about 0.75C if pollution from industry is drastically reduced. This unexpected result occurs because tiny specks from burning coal block sunlight from reaching the ground.

Preparing for the Extreme

The worst-case scenarios could be used to inform the development of long-term infrastructure, for example new towns, nuclear power stations and flood defences. Knowledge about these climate risks could also hasten the drive to reduce fossil fuel emissions.

The study formulated the severe projections using a blend of past data and records, digital projections and established principles. The possibilities exclude international cascading effects including the global food shortages and geopolitical instability.

The research was requested as part of a official risk assessment framework. Independent analyses have cautioned that not enough attention was being given to low‐likelihood but high‐impact risks.

The government's climate advisors has said that the UK must "adapt to 2C" and examine the risks for 4C. Past policy documents have been described as being "insufficient" by certain experts.

A government spokesperson said: "Global warming is at the center of the country's focus, both preparing for impacts and becoming a renewable energy leader. It is essential that the UK is resilient for the effects."