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The gravest potential impacts of the climate emergency for the UK have been detailed by researchers, encompassing a scorching 4C increase in average temperatures to a 2-metre rise in sea level. An alternative projection predicts a plunge of 6C in temperatures following the failure of critical Atlantic Ocean currents, which would severely impact agriculture and power requirements.

Plausible Events, Not Predictions

These effects, some of which are connected to irreversible climate shifts, are viewed as low probability but plausible. The scientists said that these models plugged a hole in risk assessment that had rendered the UK not ready for extreme outcomes.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are plausible," commented Nigel Arnell who led the study. "The UK has been planning lacking the methods to assess worst-case scenarios. We've now supplied decision-makers what they need to prepare for climate outcomes they wish to avoid, but must not overlook."

A Spectrum of Extreme Weather Scenarios

A further series of worst-case scenarios maps the potential extent of harsh climate between now and the end of the century. These show that thermometer readings could rocket in some months by up to 6C above the norm, while rainfall could be three times typical amounts.

The probability of the catastrophic events happening remains uncertain due to a lack of certainty about what measures will be enacted to tackle global heating and how the climate system will respond. This research was likened to defence planning or stress tests for financial systems.

Key Outcome Highlights

• Four-Degree Warming: Global temperatures rising well above 4C by 2100 could occur if climate action breaks down or if strong feedback loops including the tropical forests dying release its vast reserves of carbon. This would result in severe and lengthy heatwaves and droughts affecting the UK in summer.
• AMOC Shutdown: A major ocean current, the North Atlantic current, is losing strength and losing stability due to climate change. A full shutdown beginning in 2030 would lead to a six-degree temperature drop in the UK. "Crop production would be severely challenged and water supplies would be fundamentally reshaped," said Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in Greenland and Antarctica disintegrate quickly, inundating seaside communities. Differing from the other scenarios, this threat is already understood by infrastructure experts.
• Pollution Paradox: Global averages could also be driven up by about 0.75C if industrial aerosols is sharply cut. This paradoxical outcome occurs because pollution particles from fossil fuel combustion scatter sunlight from warming the ground.

Preparing for the Extreme

The worst-case scenarios could be utilized in planning the construction of major projects, for example new towns, nuclear power stations and flood defences. Awareness of these future hazards could also speed the drive to slash greenhouse gas emissions.

The study created the severe projections using a combination of observed and historical experience, computer simulations and scientific theory. These outcomes do not take into account international cascading effects such as the agricultural collapse and resource wars.

The project was initiated as part of a official risk assessment framework. Previous assessments have cautioned that too little consideration was being given to high-consequence, low-probability risks.

An independent advisory body has recommended that the UK needs to "become resilient to moderate heating" and examine the threats for four degrees. Previous adaptation plans have been labeled being "insufficient" by environmental groups.

A government spokesperson noted: "The climate emergency is at the core of this government’s agenda, both preparing for impacts and transitioning to a clean energy superpower. It is crucial that the UK is resilient for the effects."