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The direst projected effects of the climate crisis for the UK have been detailed by scientists, including a blistering 4C jump in temperatures to a two-metre increase in ocean levels. Another scenario predicts a plunge of 6C in temperatures following the failure of key Atlantic Ocean currents, which would massively disrupt agriculture and energy needs.

Credible Extremes, Not Predictions

These impacts, a number of which are linked to climate tipping points, are viewed as low probability but plausible. The researchers stated that these scenarios addressed a shortfall in risk assessment that had left the UK unprepared for catastrophic possibilities.

"The severe weather events we have mapped aren’t predictions, but they are possible," stated Nigel Arnell who led the research. "The nation has been formulating policy lacking the frameworks to plan for extreme possibilities. We've now given decision-makers what they need to plan for future conditions they wish to avoid, but can’t afford to ignore."

A Suite of Extreme Weather Scenarios

A second set of worst-case scenarios maps the projected severity of extreme weather between now and the year 2100. These indicate that thermometer readings could rocket in some months by up to 6C above historical levels, while precipitation could be three times normal levels.

The probability of the catastrophic events happening cannot be precisely determined due to uncertainty about what action will be implemented to combat global warming and how the planet's climate will respond. This analysis was likened to security threat evaluations or scenario planning for economic stability.

Major Possibility Elements

• 4C Temperature Rise: Planetary heating rising well above 4C by 2100 could occur if international cooperation collapses or if powerful amplifying effects like the Amazon basin dying release its huge repository of carbon. This would lead to severe and lengthy heat domes and dry spells affecting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the North Atlantic current, is losing strength and showing signs of collapse due to climate change. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Crop production would be severely challenged and freshwater availability would be drastically changed," noted the professor.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could take place if glaciers in the polar regions melt abruptly, submerging coastal cities and towns. Differing from the other scenarios, this possibility is already understood by infrastructure experts.
• Aerosol Effect: Global averages could also be driven up by about 0.75C if airborne particulates is sharply cut. This paradoxical outcome occurs because tiny specks from industrial activity block sunlight from warming the ground.

Planning for the Unthinkable

The severe models could be used to inform the building of critical national infrastructure, for example expanded cities, energy plants and urban drainage systems. Knowledge about these climate risks could also accelerate the transition to cut greenhouse gas emissions.

The research formulated the extreme models using a combination of past data and records, computer simulations and established principles. These outcomes exclude broader worldwide issues including the global food shortages and increased conflict.

The project was requested as part of a government’s adaptation planning initiative. Independent analyses have warned that too little consideration was being allocated to catastrophic yet improbable risks.

The government's climate advisors has stated that the UK needs to "prepare for two degrees of warming" and evaluate the risks for four degrees. Previous adaptation plans have been criticised as being "very weak" by environmental groups.

A national response noted: "Climate change is at the center of our national priorities, both preparing for impacts and becoming a low-carbon economy. It is essential that the UK is resilient for the consequences."