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The direst possible consequences of the climate crisis for the UK have been mapped by experts, including a searing 4C jump in average temperatures to a 2-metre rise in sea level. A separate possibility envisions a drop of 6C in temperatures following the collapse of critical Atlantic Ocean currents, which would massively disrupt agriculture and energy demand.

Possible Events, Not Forecasts

These impacts, a number of which are connected to irreversible climate shifts, are seen as improbable but credible. The team stated that these projections filled a gap in planning that had left the UK ill-prepared for worst-case results.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are possible," commented Nigel Arnell who oversaw the analysis. "The nation has been planning in the absence of the frameworks to assess worst-case scenarios. We've now provided decision-makers what they need to plan for environmental results they pray never occur, but dare not dismiss."

A Range of Harsh Climate Possibilities

A further series of severe models maps the projected severity of extreme weather between now and the year 2100. These suggest that temperatures could skyrocket in some months by up to 6C above the norm, while precipitation could be 300% of standard measurements.

The likelihood of the worst-case outcomes happening cannot be precisely determined due to uncertainty about what steps will be implemented to tackle climate change and how the planet's climate will react. This analysis was likened to security threat evaluations or scenario planning for the banking sector.

Major Outcome Elements

• Severe Heating: Global temperatures soaring past 4C by 2100 could happen if international cooperation breaks down or if powerful amplifying effects such as the tropical forests becoming a net carbon source unleash its vast reserves of carbon. This would cause intense and enduring heat domes and water shortages plaguing the UK in summer.
• Atlantic Current Collapse: A major ocean current, the North Atlantic current, is slowing down and becoming unstable due to ocean warming. A complete failure commencing by 2030 would lead to a 6C cooling in the UK. "Crop production would be severely challenged and freshwater availability would be completely altered," explained the lead researcher.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in the Arctic and Antarctic disintegrate quickly, submerging low-lying areas. Differing from the other scenarios, this possibility is already understood by coastal engineers.
• Clean Air Warming: Global averages could also be increased by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because tiny specks from fossil fuel combustion scatter sunlight from reaching the ground.

Planning for the Extreme

The worst-case scenarios could be utilized in planning the development of critical national infrastructure, including new towns, power generation facilities and flood defences. Knowledge about these future hazards could also hasten the push to reduce greenhouse gas emissions.

The study created the severe projections using a mix of real-world events, computer simulations and scientific theory. The possibilities do not take into account international cascading effects including the global food shortages and geopolitical instability.

The research was initiated as part of a national risk assessment framework. Earlier reports have warned that too little consideration was being allocated to high-consequence, low-probability risks.

The government's climate advisors has recommended that the UK needs to "prepare for two degrees of warming" and examine the threats for severe warming. Earlier government strategies have been labeled being "very weak" by certain experts.

A national response said: "Climate change is at the heart of the country's focus, both adapting for the future and transitioning to a renewable energy leader. It is vital that the UK is prepared for the effects."