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The most severe projected effects of the global heating for the UK have been mapped by scientists, encompassing a blistering 4C jump in temperatures to a two-metre increase in sea levels. A separate possibility predicts a decline of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would severely impact farming and power requirements.

Possible Outcomes, Not Forecasts

These impacts, certain ones are associated with critical climate thresholds, are considered as unlikely but credible. The team explained that these projections plugged a hole in planning that had left the UK unprepared for catastrophic possibilities.

"The worst-case scenarios we have detailed should not be seen as certainties, but they are possible," said the professor who directed the analysis. "The UK has been planning in the absence of the methods to test against catastrophic outcomes. We've now given planners what they need to prepare for future conditions they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Possibilities

A second set of severe models maps the possible scale of extreme weather between now and the year 2100. These show that thermometer readings could skyrocket in certain periods by up to 6C higher than the norm, while precipitation could be triple typical amounts.

The likelihood of the extreme scenarios coming to pass could not be calculated due to uncertainty about what measures will be implemented to address climate change and how the Earth's systems will respond. This research was compared to national security risk assessments or stress tests for financial systems.

Key Possibility Elements

• Severe Heating: Planetary heating soaring past 4C by 2100 could transpire if international cooperation fails or if strong feedback loops including the Amazon rainforest perishing emit its vast reserves of carbon. This would lead to intense and enduring heat domes and droughts affecting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the North Atlantic current, is losing strength and showing signs of collapse due to global heating. A complete failure commencing by 2030 would lead to a drastic cooling in the UK. "Agriculture would struggle enormously and freshwater availability would be completely altered," explained Arnell.
• Rapid Sea Level Rise: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in Greenland and Antarctica melt abruptly, inundating seaside communities. In contrast to the other scenarios, this threat is already known by planners.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if airborne particulates is sharply cut. This paradoxical outcome occurs because pollution particles from fossil fuel combustion block sunlight from warming the ground.

Planning for the Worst

These dire projections could be used to inform the building of long-term infrastructure, including new towns, energy plants and flood defences. Awareness of these climate risks could also hasten the push to reduce fossil fuel emissions.

The research formulated the worst-case scenarios using a combination of real-world events, digital projections and scientific theory. The possibilities do not take into account broader worldwide issues like the global food shortages and resource wars.

This work was commissioned as part of a national adaptation planning initiative. Previous assessments have stated that insufficient focus was being allocated to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK needs to "adapt to 2C" and evaluate the risks for 4C. Earlier government strategies have been described as being "insufficient" by environmental groups.

A government spokesperson noted: "Global warming is at the center of our national priorities, both preparing for impacts and establishing itself as a renewable energy leader. It is crucial that the UK is prepared for the consequences."