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The gravest potential impacts of the climate crisis for the UK have been mapped by researchers, encompassing a blistering 4C rise in temperatures to a 2-metre rise in sea level. A separate possibility predicts a plunge of 6C in temperatures following the failure of crucial Atlantic Ocean currents, which would severely impact food production and energy needs.

Possible Events, Not Predictions

These impacts, a number of which are connected to climate tipping points, are viewed as unlikely but plausible. The researchers said that these models filled a gap in risk assessment that had left the UK ill-prepared for worst-case results.

"The severe weather events we have detailed should not be seen as certainties, but they are credible," said the professor who directed the research. "Britain has been formulating policy in the absence of the frameworks to test against extreme possibilities. We've now provided planners what they need to get ready for future conditions they pray never occur, but must not overlook."

A Range of Extreme Weather Possibilities

Another collection of severe models maps the potential extent of severe conditions between now and the end of the century. These show that thermometer readings could soar in particular seasons by up to 6C above the norm, while rainfall could be 300% of normal levels.

The probability of the worst-case outcomes occurring cannot be precisely determined due to unknown factors about what steps will be enacted to address global heating and how the climate system will react. This approach was likened to national security risk assessments or stress tests for financial systems.

Key Scenario Highlights

• Severe Heating: Planetary heating exceeding 4C by 2100 could happen if climate action collapses or if strong feedback loops such as the Amazon rainforest perishing unleash its huge repository of carbon. This would lead to severe and lengthy heat domes and water shortages hitting the UK in summer.
• AMOC Shutdown: A key circulation system, the AMOC, is slowing down and losing stability due to climate change. A complete failure beginning in 2030 would lead to a drastic cooling in the UK. "Farming would struggle enormously and freshwater availability would be fundamentally reshaped," noted the professor.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic disintegrate quickly, submerging coastal cities and towns. Differing from the other scenarios, this possibility is already understood by planners.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if pollution from industry is drastically reduced. This counterintuitive effect occurs because aerosol particles from fossil fuel combustion block sunlight from warming the ground.

Preparing for the Extreme

The worst-case scenarios could be used to inform the building of critical national infrastructure, for example expanded cities, power generation facilities and flood defences. Awareness of these future hazards could also speed the transition to cut fossil fuel emissions.

The analysis formulated the severe projections using a blend of real-world events, digital projections and climate physics. The possibilities omit international cascading effects including the devastation of food supplies and resource wars.

This work was requested as part of a national risk assessment framework. Independent analyses have warned that too little consideration was being allocated to catastrophic yet improbable risks.

An independent advisory body has stated that the UK needs to "become resilient to moderate heating" and assess the dangers for four degrees. Earlier government strategies have been criticised as being "very weak" by some observers.

A national response noted: "Climate change is at the core of the country's focus, both building resilience and establishing itself as a low-carbon economy. It is crucial that the UK is ready for the impacts."