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The gravest projected effects of the climate crisis for the UK have been outlined by scientists, ranging from a searing 4C rise in average temperatures to a 2-metre surge in ocean levels. Another scenario predicts a drop of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Plausible Outcomes, Not Guarantees

These effects, certain ones are associated with climate tipping points, are considered as low probability but possible. The scientists stated that these scenarios addressed a shortfall in forecasting that had rendered the UK not ready for catastrophic possibilities.

"The severe weather events we have mapped are not forecasts, but they are possible," commented the professor who directed the analysis. "The UK has been making preparations without the frameworks to plan for catastrophic outcomes. We've now supplied decision-makers what they need to get ready for environmental results they hope never happen, but can’t afford to ignore."

A Suite of Extreme Weather Possibilities

Another collection of worst-case scenarios sets out the possible scale of extreme weather between now and the end of the century. These indicate that thermometer readings could soar in some months by up to 6C above the norm, while rainfall could be 300% of standard measurements.

The chance of the worst-case outcomes happening remains uncertain due to uncertainty about what action will be taken to address global heating and how the climate system will respond. This approach was described as similar to security threat evaluations or stress tests for financial systems.

Critical Possibility Highlights

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could happen if climate action collapses or if strong feedback loops including the tropical forests dying unleash its huge repository of carbon. This would cause intense and enduring heatwaves and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is weakening and showing signs of collapse due to ocean warming. A complete failure commencing by 2030 would lead to a 6C cooling in the UK. "Agriculture would be severely challenged and water resources would be drastically changed," noted the lead researcher.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica melt abruptly, flooding seaside communities. In contrast to the other scenarios, this risk is already understood by infrastructure experts.
• Clean Air Warming: Global averages could also be pushed higher by about 0.75C if industrial aerosols is rapidly cleaned up. This paradoxical outcome occurs because aerosol particles from industrial activity scatter solar radiation from warming the ground.

Planning for the Worst

These dire projections could be utilized in planning the development of critical national infrastructure, including expanded cities, nuclear power stations and flood defences. Understanding these future hazards could also accelerate the push to cut fossil fuel emissions.

The study developed the severe projections using a blend of observed and historical experience, computer simulations and climate physics. These outcomes omit international cascading effects such as the global food shortages and resource wars.

The research was commissioned as part of a government’s adaptation planning initiative. Independent analyses have stated that insufficient focus was being given to low‐likelihood but high‐impact risks.

The government's climate advisors has stated that the UK must "become resilient to moderate heating" and evaluate the threats for 4C. Previous adaptation plans have been described as being "inadequate" by environmental groups.

An official statement said: "The climate emergency is at the core of the country's focus, both preparing for impacts and becoming a low-carbon economy. It is vital that the UK is ready for the consequences."