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The most severe possible consequences of the climate emergency for the UK have been detailed by scientists, encompassing a searing 4C increase in temperatures to a 6.5-foot surge in sea levels. An alternative projection envisions a drop of 6C in temperatures following the failure of key Atlantic Ocean currents, which would profoundly upset food production and energy demand.

Plausible Extremes, Not Predictions

These consequences, certain ones are connected to irreversible climate shifts, are seen as low probability but plausible. The team stated that these scenarios plugged a hole in planning that had left the UK ill-prepared for catastrophic possibilities.

"The worst-case scenarios we have mapped aren’t predictions, but they are possible," stated the professor who directed the research. "The UK has been formulating policy without the frameworks to plan for worst-case scenarios. We've now supplied policymakers what they need to plan for climate outcomes they wish to avoid, but can’t afford to ignore."

A Suite of Severe Conditions Possibilities

A second set of dire projections details the potential extent 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 higher than average, while precipitation could be three times typical amounts.

The probability of the catastrophic events happening cannot be precisely determined due to a lack of certainty about what steps will be implemented to tackle global heating and how the Earth's systems will behave. This approach was likened to security threat evaluations or stress tests for the banking sector.

Key Scenario Elements

• Four-Degree Warming: Global temperatures soaring past 4C by 2100 could occur if emissions cuts collapses or if powerful amplifying effects including the Amazon rainforest dying unleash its vast reserves of carbon. This would result in intense and enduring heatwaves and droughts affecting the UK in summer.
• Ocean Circulation Failure: A major ocean current, the AMOC, is weakening and showing signs of collapse due to global heating. A full shutdown commencing by 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and water supplies would be drastically changed," explained Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in the polar regions collapse rapidly, submerging low-lying areas. Differing from the other scenarios, this possibility is already recognized by planners.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if airborne particulates is drastically reduced. This paradoxical outcome occurs because tiny specks from fossil fuel combustion reflect solar radiation from warming the ground.

Planning for the Extreme

The severe models could be applied to guide the development of long-term infrastructure, such as new towns, nuclear power stations and urban drainage systems. Knowledge about these environmental threats could also speed the transition to cut greenhouse gas emissions.

The study developed the extreme models using a mix of past data and records, digital projections and scientific theory. The possibilities omit potential global problems including the agricultural collapse and resource wars.

The project was commissioned as part of a government’s risk assessment framework. Independent analyses have stated that too little consideration was being allocated to low‐likelihood but high‐impact risks.

The government's climate advisors has said that the UK must "prepare for two degrees of warming" and assess the risks for 4C. Previous adaptation plans have been labeled being "inadequate" by some observers.

A government spokesperson said: "Climate change is at the center of this government’s agenda, both building resilience and establishing itself as a clean energy superpower. It is essential that the UK is resilient for the consequences."