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The most severe potential impacts of the global heating for the UK have been detailed by scientists, ranging from a blistering 4C rise in mean temperatures to a two-metre increase in sea level. An alternative projection envisions a decline of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would massively disrupt food production and energy needs.

Possible Events, Not Guarantees

These impacts, certain ones are linked to critical climate thresholds, are seen as improbable but plausible. The team said that these projections filled a gap in risk assessment that had left the UK not ready for worst-case results.

"The climate extremes we have outlined are not forecasts, but they are credible," commented the professor who directed the research. "The nation has been making preparations in the absence of the tools to assess extreme possibilities. We've now given policymakers what they need to plan for climate outcomes they wish to avoid, but must not overlook."

A Range of Extreme Weather Possibilities

Another collection of worst-case scenarios sets out the potential extent of severe conditions between now and the year 2100. These suggest that temperatures could rocket in some months by up to 6C above historical levels, while precipitation could be triple typical amounts.

The probability of the extreme scenarios happening could not be calculated due to uncertainty about what steps will be enacted to combat climate change and how the planet's climate will behave. This research was likened to national security risk assessments or resilience checks for the banking sector.

Key Outcome Elements

• Severe Heating: Planetary heating rising well above 4C by 2100 could transpire if international cooperation collapses or if powerful amplifying effects such as the tropical forests perishing release its enormous store of carbon. This would lead to intense and enduring heatwaves and water shortages hitting the UK in summer.
• AMOC Shutdown: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and showing signs of collapse due to climate change. A complete failure beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would face immense difficulties and water resources would be drastically changed," noted Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the polar regions collapse rapidly, submerging low-lying areas. Differing from the other scenarios, this threat is already recognized by planners.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if industrial aerosols is sharply cut. This counterintuitive effect occurs because pollution particles from fossil fuel combustion block sunlight from reaching the ground.

Preparing for the Worst

The severe models could be used to inform the construction of major projects, for example new towns, energy plants and flood defences. Knowledge about these climate risks could also accelerate the transition to cut fossil fuel emissions.

The study formulated the severe projections using a combination of observed and historical experience, digital projections and established principles. The possibilities omit international cascading effects including the agricultural collapse and increased conflict.

This work was initiated as part of a government’s adaptation planning initiative. Independent analyses have cautioned that not enough attention was being paid to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK must "adapt to 2C" and examine the risks for four degrees. Earlier government strategies have been criticised as being "inadequate" by some observers.

A government spokesperson commented: "Climate change is at the center of this government’s agenda, both preparing for impacts and becoming a clean energy superpower. It is crucial that the UK is ready for the consequences."