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The most severe projected effects of the climate emergency for the UK have been detailed by scientists, ranging from a blistering 4C rise in average temperatures to a 2-metre rise in sea levels. Another scenario foresees a drop of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would profoundly upset farming and energy demand.

Credible Extremes, Not Forecasts

These effects, a number of which are connected to climate tipping points, are seen as unlikely but possible. The team explained that these projections plugged a hole in forecasting that had rendered the UK not ready for worst-case results.

"The severe weather events we have detailed aren’t predictions, but they are plausible," stated the lead researcher who led the research. "The UK has been planning in the absence of the tools to test against extreme possibilities. We've now supplied planners what they need to get ready for environmental results they pray never occur, but must not overlook."

A Suite of Severe Conditions Projections

A second set of worst-case scenarios details the potential extent of severe conditions between now and the close of the 2100s. These show that temperatures could skyrocket in particular seasons by up to 6C higher than average, while precipitation could be triple typical amounts.

The likelihood of the worst-case outcomes coming to pass remains uncertain due to a lack of certainty about what action will be enacted to combat global heating and how the planet's climate will react. This approach was compared to national security risk assessments or stress tests for economic stability.

Critical Scenario Highlights

• Four-Degree Warming: Planetary heating soaring past 4C by 2100 could happen if emissions cuts collapses or if vicious cycles including the tropical forests becoming a net carbon source release its vast reserves of carbon. This would result in intense and enduring heat domes and dry spells affecting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is weakening and losing stability due to global heating. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Crop production would struggle enormously and freshwater availability would be fundamentally reshaped," explained Arnell.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in Greenland and Antarctica collapse rapidly, flooding coastal cities and towns. Differing from the other scenarios, this threat is already known by infrastructure experts.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if pollution from industry is rapidly cleaned up. This paradoxical outcome occurs because aerosol particles from burning coal reflect solar radiation from reaching the ground.

Building Resilience Against the Worst

The severe models could be applied to guide the construction of major projects, including expanded cities, nuclear power stations and flood defences. Awareness of these climate risks could also accelerate the transition to slash carbon pollution.

The analysis developed the severe projections using a combination of past data and records, computer simulations and scientific theory. The possibilities omit broader worldwide issues including the devastation of food supplies and increased conflict.

This work was initiated as part of a official risk assessment framework. Previous assessments have warned that not enough attention was being paid to high-consequence, low-probability risks.

Official experts has recommended that the UK must "become resilient to moderate heating" and evaluate the threats for 4C. Earlier government strategies have been described as being "insufficient" by certain experts.

An official statement noted: "Global warming is at the center of the country's focus, both building resilience and transitioning to a renewable energy leader. It is crucial that the UK is resilient for the impacts."