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The gravest potential impacts of the climate crisis for the UK have been detailed by scientists, including a scorching 4C increase in average temperatures to a 2-metre surge in sea level. A separate possibility envisions a decline of 6C in temperature following the failure of crucial Atlantic Ocean currents, which would profoundly upset food production and energy needs.

Plausible Events, Not Predictions

These effects, a number of which are linked to climate tipping points, are seen as unlikely but plausible. The researchers stated that these projections plugged a hole in forecasting that had rendered the UK unprepared for extreme outcomes.

"The worst-case scenarios we have detailed aren’t predictions, but they are credible," stated the professor who directed the analysis. "The UK has been making preparations in the absence of the frameworks to plan for worst-case scenarios. We've now supplied policymakers what they need to get ready for environmental results they pray never occur, but must not overlook."

A Range of Harsh Climate Scenarios

A second set of severe models details the possible scale of extreme weather between now and the year 2100. These indicate that thermometer readings could skyrocket in particular seasons by up to 6C higher than historical levels, while rainfall could be three times typical amounts.

The likelihood of the extreme scenarios occurring could not be calculated due to uncertainty about what measures will be implemented to tackle global heating and how the Earth's systems will behave. This analysis was likened to defence planning or resilience checks for financial systems.

Major Scenario Highlights

• Severe Heating: Planetary heating soaring past 4C by 2100 could transpire if climate action collapses or if strong feedback loops such as the Amazon basin perishing unleash its vast reserves of carbon. This would cause intense and enduring heat domes and water shortages affecting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the North Atlantic current, is slowing down and losing stability due to ocean warming. A complete failure beginning in 2030 would lead to a six-degree temperature drop in the UK. "Crop production would struggle enormously and water resources would be completely altered," explained Arnell.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in Greenland and Antarctica disintegrate quickly, inundating coastal cities and towns. Unlike the other scenarios, this possibility is already understood by infrastructure experts.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if pollution from industry is sharply cut. This unexpected result occurs because pollution particles from fossil fuel combustion reflect sunlight from reaching the ground.

Preparing for the Worst

The severe models could be applied to guide the development of long-term infrastructure, for example expanded cities, energy plants and flood defences. Knowledge about these environmental threats could also hasten the drive to reduce greenhouse gas emissions.

The study formulated the extreme models using a combination of past data and records, climate models and scientific theory. The possibilities do not take into account international cascading effects like the devastation of food supplies and increased conflict.

The research was initiated as part of a national 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 said that the UK must "adapt to 2C" and evaluate the risks for severe warming. Earlier government strategies have been described as being "insufficient" by certain experts.

A national response said: "Climate change is at the heart of this government’s agenda, both building resilience and establishing itself as a low-carbon economy. It is essential that the UK is ready for the effects."