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The direst projected effects of the climate emergency for the UK have been outlined by scientists, including a scorching 4C rise in average temperatures to a 2-metre rise in ocean levels. An alternative projection predicts a decline of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would massively disrupt food production and energy demand.

Plausible Extremes, Not Forecasts

These consequences, a number of which are linked to critical climate thresholds, are seen as low probability but plausible. The researchers said that these projections addressed a shortfall in forecasting that had rendered the UK unprepared for worst-case results.

"The worst-case scenarios we have detailed aren’t predictions, but they are plausible," stated the professor who directed the research. "Britain has been planning in the absence of the tools to plan for extreme possibilities. We've now supplied policymakers what they need to get ready for future conditions they wish to avoid, but must not overlook."

A Range of Harsh Climate Projections

A further series of dire projections details the projected severity of extreme weather between now and the end of the century. These suggest that thermometer readings could skyrocket in particular seasons by up to 6C above the norm, while precipitation could be 300% of standard measurements.

The probability of the extreme scenarios occurring cannot be precisely determined due to unknown factors about what action will be enacted to combat climate change and how the Earth's systems will respond. This approach was likened to defence planning or scenario planning for economic stability.

Key Possibility Highlights

• Severe Heating: Worldwide averages rising well above 4C by 2100 could occur if international cooperation collapses or if vicious cycles including the tropical forests becoming a net carbon source unleash its huge repository of carbon. This would cause severe and lengthy heatwaves and water shortages hitting the UK in summer.
• AMOC Shutdown: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is losing strength and showing signs of collapse due to global heating. A complete failure starting around 2030 would lead to a 6C cooling in the UK. "Agriculture would face immense difficulties and freshwater availability would be fundamentally reshaped," explained Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the polar regions melt abruptly, inundating seaside communities. Unlike the other scenarios, this possibility is already understood by planners.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if pollution from industry is rapidly cleaned up. This paradoxical outcome occurs because tiny specks from fossil fuel combustion scatter solar radiation from warming the ground.

Preparing for the Extreme

The severe models could be used to inform the building of major projects, for example housing developments, nuclear power stations and urban drainage systems. Understanding these future hazards could also accelerate the push to slash fossil fuel emissions.

The analysis developed the worst-case scenarios using a blend of past data and records, climate models and scientific theory. The possibilities omit broader worldwide issues including the agricultural collapse and increased conflict.

The research was requested as part of a official climate resilience programme. Previous assessments have warned that insufficient focus was being paid to catastrophic yet improbable risks.

The government's climate advisors has said that the UK needs to "become resilient to moderate heating" and examine the risks for 4C. Earlier government strategies have been labeled being "inadequate" by environmental groups.

An official statement noted: "Global warming is at the core of our national priorities, both building resilience and establishing itself as a clean energy superpower. It is vital that the UK is prepared for the effects."