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The direst potential impacts of the global heating for the UK have been mapped by scientists, encompassing a scorching 4C rise in mean temperatures to a 6.5-foot rise in sea level. An alternative projection predicts a plunge of 6C in temperature following the failure of critical Atlantic Ocean currents, which would severely impact agriculture and energy needs.

Possible Events, Not Predictions

These effects, certain ones are linked to critical climate thresholds, are seen as improbable but plausible. The researchers stated that these models addressed a shortfall in risk assessment that had left the UK unprepared for worst-case results.

"The climate extremes we have outlined are not forecasts, but they are possible," commented Nigel Arnell who oversaw the research. "The UK has been planning in the absence of the methods to plan for extreme possibilities. We've now supplied policymakers what they need to get ready for future conditions they wish to avoid, but must not overlook."

A Range of Harsh Climate Scenarios

Another collection of worst-case scenarios sets out the potential extent of harsh climate between now and the year 2100. These suggest that temperatures could soar in some months by up to 6C above historical levels, while rainfall could be three times normal levels.

The chance of the worst-case outcomes occurring could not be calculated due to unknown factors about what measures will be enacted to combat global heating and how the climate system will react. This research was likened to national security risk assessments or stress tests for economic stability.

Critical Possibility Details

• Severe Heating: Planetary heating exceeding 4C by 2100 could happen if international cooperation fails or if powerful amplifying effects like the Amazon basin becoming a net carbon source emit its huge repository of carbon. This would result in extreme and prolonged heatwaves and water shortages affecting the UK in summer.
• Ocean Circulation Failure: A major ocean current, the AMOC, is weakening and showing signs of collapse due to global heating. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Farming would be severely challenged and water resources would be drastically changed," said Arnell.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in Greenland and Antarctica 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 pushed higher by about 0.75C if pollution from industry is drastically reduced. This unexpected result occurs because pollution particles from fossil fuel combustion reflect sunlight from warming the ground.

Building Resilience Against the Worst

The severe models could be applied to guide the building of critical national infrastructure, including new towns, energy plants and urban drainage systems. Knowledge about these climate risks could also accelerate the push to slash greenhouse gas emissions.

The research formulated the severe projections using a blend of past data and records, computer simulations and established principles. These outcomes exclude potential global problems like the agricultural collapse and increased conflict.

The research was initiated as part of a official adaptation planning initiative. Earlier reports have stated that not enough attention was being paid to catastrophic yet improbable risks.

Official experts has said that the UK must "prepare for two degrees of warming" and assess the risks for 4C. Past policy documents have been criticised as being "inadequate" by certain experts.

A national response said: "Global warming is at the core of the country's focus, both preparing for impacts and becoming a renewable energy leader. It is crucial that the UK is resilient for the consequences."