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The gravest potential impacts of the climate emergency for the UK have been detailed by experts, including a blistering 4C jump in mean temperatures to a two-metre rise in ocean levels. An alternative projection predicts a decline of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would massively disrupt farming and energy needs.

Plausible Outcomes, Not Guarantees

These impacts, a number of which are linked to climate tipping points, are viewed as unlikely but possible. The scientists explained that these projections filled a gap in forecasting that had left the UK unprepared for extreme outcomes.

"The severe weather events we have mapped are not forecasts, but they are possible," said the lead researcher who oversaw the analysis. "The UK has been formulating policy lacking the tools to plan for extreme possibilities. We've now given policymakers what they need to get ready for future conditions they hope never happen, but dare not dismiss."

A Range of Severe Conditions Projections

A second set of worst-case scenarios sets out the potential extent of harsh climate between now and the close of the 2100s. These indicate that temperatures could soar in some months by up to 6C higher than average, while rainfall could be triple typical amounts.

The chance of the extreme scenarios coming to pass cannot be precisely determined due to unknown factors about what action will be enacted to address climate change and how the planet's climate will behave. This research was compared to national security risk assessments or stress tests for economic stability.

Major Outcome Details

• Four-Degree Warming: Planetary heating exceeding 4C by 2100 could transpire if climate action collapses or if vicious cycles like the tropical forests perishing unleash its vast reserves of carbon. This would cause extreme and prolonged 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 ocean warming. A complete failure commencing by 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would be severely challenged and water supplies would be completely altered," explained the lead researcher.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in Greenland and Antarctica collapse rapidly, flooding low-lying areas. In contrast to the other scenarios, this threat is already recognized by infrastructure experts.
• Pollution Paradox: Temperatures 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.

Planning 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 urban drainage systems. Understanding these climate risks could also speed the drive to slash greenhouse gas emissions.

The analysis created the worst-case scenarios using a blend of real-world events, digital projections and scientific theory. The scenarios exclude broader worldwide issues such as the agricultural collapse and geopolitical instability.

This work was initiated as part of a official risk assessment framework. Earlier reports have cautioned that insufficient focus was being given to low‐likelihood but high‐impact risks.

Official experts has recommended that the UK must "become resilient to moderate heating" and examine the dangers for 4C. Earlier government strategies have been described as being "inadequate" by environmental groups.

An official statement said: "Global warming is at the core of this government’s agenda, both adapting for the future and establishing itself as a low-carbon economy. It is vital that the UK is ready for the effects."