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The gravest possible consequences of the climate emergency for the UK have been outlined by experts, including a searing 4C jump in temperatures to a two-metre surge in ocean levels. A separate possibility envisions a drop of 6C in temperature following the failure of key Atlantic Ocean currents, which would massively disrupt agriculture and energy demand.

Possible Extremes, Not Predictions

These impacts, a number of which are connected to climate tipping points, are considered as improbable but possible. The team said that these projections addressed a shortfall in forecasting that had left the UK not ready for worst-case results.

"The severe weather events we have mapped should not be seen as certainties, but they are credible," stated the professor who oversaw the research. "The UK has been formulating policy without the frameworks to assess worst-case scenarios. We've now given decision-makers what they need to plan for climate outcomes they pray never occur, but dare not dismiss."

A Range of Harsh Climate Scenarios

A further series of severe models sets out the projected severity of harsh climate between now and the close of the 2100s. These indicate that temperatures could soar in particular seasons by up to 6C higher than average, while precipitation could be triple normal levels.

The chance of the extreme scenarios coming to pass could not be calculated due to unknown factors about what action will be enacted to address climate change and how the planet's climate will react. This research was described as similar to national security risk assessments or scenario planning for financial systems.

Critical Outcome Highlights

• 4C Temperature Rise: Global temperatures soaring past 4C by 2100 could occur if international cooperation collapses or if strong feedback loops including the Amazon basin becoming a net carbon source emit its vast reserves of carbon. This would result in intense and enduring heatwaves and dry spells hitting the UK in summer.
• AMOC Shutdown: A major ocean current, the AMOC, is losing strength and becoming unstable due to ocean warming. A collapse starting around 2030 would lead to a drastic cooling in the UK. "Crop production would be severely challenged and freshwater availability would be drastically changed," noted Arnell.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic disintegrate quickly, inundating low-lying areas. Differing from the other scenarios, this risk is already known by planners.
• Clean Air Warming: Global averages could also be increased by about 0.75C if industrial aerosols is rapidly cleaned up. This paradoxical outcome occurs because tiny specks from industrial activity scatter solar radiation from reaching the ground.

Planning for the Worst

The worst-case scenarios could be used to inform the building of critical national infrastructure, for example new towns, power generation facilities and urban drainage systems. Awareness of these environmental threats could also hasten the transition to slash fossil fuel emissions.

The study developed the severe projections using a mix of observed and historical experience, computer simulations and scientific theory. These outcomes omit international cascading effects such as the agricultural collapse and resource wars.

This work was commissioned as part of a official climate resilience programme. Independent analyses have warned that insufficient focus was being allocated to low‐likelihood but high‐impact risks.

Official experts has recommended that the UK must "become resilient to moderate heating" and evaluate the threats for four degrees. Past policy documents have been criticised as being "very weak" by some observers.

A national response said: "The climate emergency is at the center of the country's focus, both preparing for impacts and establishing itself as a clean energy superpower. It is vital that the UK is resilient for the effects."