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The most severe potential impacts of the climate crisis for the UK have been outlined by scientists, ranging from a blistering 4C jump in mean temperatures to a 2-metre surge in sea level. A separate possibility foresees a decline of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would severely impact agriculture and energy needs.

Possible Events, Not Forecasts

These impacts, certain ones are linked to critical climate thresholds, are viewed as low probability but plausible. The team explained that these models plugged a hole in risk assessment that had left the UK not ready for catastrophic possibilities.

"The severe weather events we have outlined should not be seen as certainties, but they are possible," said Nigel Arnell who directed the research. "The UK has been making preparations without the methods to plan for extreme possibilities. We've now provided decision-makers what they need to prepare for environmental results they pray never occur, but dare not dismiss."

A Range of Severe Conditions Scenarios

A further series of severe models sets out the possible scale of severe conditions between now and the end of the century. These suggest that thermometer readings could soar in some months by up to 6C above average, while rainfall could be 300% of typical amounts.

The probability of the extreme scenarios happening could not be calculated due to unknown factors about what measures will be enacted to combat global heating and how the Earth's systems will behave. This approach was compared to security threat evaluations or stress tests for financial systems.

Major Scenario Details

• 4C Temperature Rise: Global temperatures exceeding 4C by 2100 could occur if climate action fails or if vicious cycles including the Amazon rainforest becoming a net carbon source unleash its vast reserves of carbon. This would result in extreme and prolonged heatwaves and dry spells hitting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the AMOC, is losing strength and becoming unstable due to climate change. A full shutdown starting around 2030 would lead to a 6C cooling in the UK. "Farming would struggle enormously and freshwater availability would be completely altered," noted the lead researcher.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could happen if ice sheets in Greenland and Antarctica collapse rapidly, submerging low-lying areas. Unlike the other scenarios, this possibility is already understood by planners.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if industrial aerosols is sharply cut. This paradoxical outcome occurs because aerosol particles from burning coal reflect sunlight from warming the ground.

Building Resilience Against the Unthinkable

The worst-case scenarios could be utilized in planning the development of long-term infrastructure, for example housing developments, power generation facilities and urban drainage systems. Knowledge about these future hazards could also speed the drive to reduce fossil fuel emissions.

The study formulated the worst-case scenarios using a mix of past data and records, digital projections and established principles. The possibilities omit broader worldwide issues including the agricultural collapse and resource wars.

The research was requested as part of a government’s adaptation planning initiative. Earlier reports have cautioned that too little consideration was being given to high-consequence, low-probability risks.

The government's climate advisors has said that the UK must "adapt to 2C" and evaluate the dangers for 4C. Earlier government strategies have been labeled being "inadequate" by some observers.

An official statement said: "The climate emergency is at the center of our national priorities, both building resilience and transitioning to a renewable energy leader. It is vital that the UK is prepared for the consequences."