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The direst possible consequences of the global heating for the UK have been mapped by researchers, including a scorching 4C rise in temperatures to a two-metre surge in ocean levels. A separate possibility predicts a drop of 6C in temperature following the failure of key Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Possible Extremes, Not Predictions

These effects, some of which are connected to critical climate thresholds, are considered as low probability but possible. The team said that these models filled a gap in planning that had left the UK not ready for extreme outcomes.

"The climate extremes we have mapped aren’t predictions, but they are credible," commented Nigel Arnell who directed the research. "The nation has been making preparations lacking the frameworks to assess catastrophic outcomes. We've now supplied planners what they need to prepare for climate outcomes they wish to avoid, but must not overlook."

A Range of Harsh Climate Possibilities

Another collection of severe models maps the projected severity of severe conditions between now and the close of the 2100s. These suggest that thermometer readings could rocket in certain periods by up to 6C above average, while precipitation could be three times typical amounts.

The chance of the worst-case outcomes happening remains uncertain due to uncertainty about what measures will be enacted to address climate change and how the climate system will react. This research was compared to defence planning or scenario planning for financial systems.

Critical Scenario Details

• Severe Heating: Worldwide averages soaring past 4C by 2100 could happen if international cooperation collapses or if strong feedback loops like the Amazon rainforest perishing emit its huge repository of carbon. This would cause intense and enduring heatwaves and water shortages plaguing the UK in summer.
• Ocean Circulation Failure: A critical sea current, the North Atlantic current, is losing strength and showing signs of collapse due to global heating. A complete failure starting around 2030 would lead to a six-degree temperature drop in the UK. "Crop production would struggle enormously and freshwater availability would be drastically changed," said Arnell.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could occur if glaciers in Greenland and Antarctica melt abruptly, submerging coastal cities and towns. Differing from the other scenarios, this threat is already recognized by planners.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from fossil fuel combustion scatter solar radiation from reaching the ground.

Building Resilience Against the Extreme

The severe models could be applied to guide the construction of major projects, including housing developments, energy plants and urban drainage systems. Knowledge about these climate risks could also hasten the drive to reduce fossil fuel emissions.

The analysis formulated the worst-case scenarios using a blend of real-world events, climate models and established principles. These outcomes do not take into account international cascading effects including the global food shortages and resource wars.

The research was requested as part of a official climate resilience programme. Previous assessments have stated that not enough attention was being allocated to low‐likelihood but high‐impact risks.

An independent advisory body has recommended that the UK needs to "become resilient to moderate heating" and assess the risks for severe warming. Previous adaptation plans have been labeled being "inadequate" by some observers.

A national response said: "Global warming is at the heart of the country's focus, both preparing for impacts and becoming a clean energy superpower. It is crucial that the UK is resilient for the impacts."