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The most severe potential impacts of the climate crisis for the UK have been detailed by researchers, including a scorching 4C rise in temperatures to a 2-metre increase in sea level. Another scenario predicts a plunge of 6C in temperature following the collapse of key Atlantic Ocean currents, which would profoundly upset food production and power requirements.

Possible Outcomes, Not Predictions

These impacts, a number of which are associated with climate tipping points, are seen as unlikely but plausible. The team said that these projections plugged a hole in risk assessment that had rendered the UK not ready for worst-case results.

"The severe weather events we have outlined are not forecasts, but they are possible," commented the lead researcher who led the research. "The UK has been making preparations in the absence of the tools to plan for catastrophic outcomes. We've now supplied decision-makers what they need to prepare for future conditions they hope never happen, but can’t afford to ignore."

A Spectrum of Harsh Climate Projections

Another collection of dire projections maps the projected severity of severe conditions between now and the close of the 2100s. These show that temperatures could skyrocket in certain periods by up to 6C above average, while precipitation could be triple standard measurements.

The likelihood of the worst-case outcomes occurring remains uncertain due to a lack of certainty about what action will be implemented to tackle climate change and how the planet's climate will react. This research was compared to security threat evaluations or stress tests for the banking sector.

Key Possibility Elements

• 4C Temperature Rise: Planetary heating rising well above 4C by 2100 could occur if climate action collapses or if powerful amplifying effects such as the Amazon rainforest becoming a net carbon source unleash its vast reserves of carbon. This would lead to intense and enduring heatwaves and dry spells hitting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the AMOC, is losing strength and showing signs of collapse due to global heating. A complete failure beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would be severely challenged and freshwater availability would be fundamentally reshaped," explained Arnell.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in Greenland and Antarctica melt abruptly, flooding seaside communities. Unlike the other scenarios, this risk is already recognized by infrastructure experts.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if airborne particulates is rapidly cleaned up. This unexpected result occurs because pollution particles from fossil fuel combustion block sunlight from reaching the ground.

Preparing for the Extreme

The worst-case scenarios could be applied to guide the development of critical national infrastructure, including expanded cities, nuclear power stations and flood defences. Awareness of these environmental threats could also hasten the transition to cut fossil fuel emissions.

The research created the worst-case scenarios using a combination of past data and records, digital projections and established principles. These outcomes exclude potential global problems like the devastation of food supplies and geopolitical instability.

The project was requested as part of a national adaptation planning initiative. Previous assessments have warned that not enough attention was being allocated to catastrophic yet improbable risks.

The government's climate advisors has said that the UK must "adapt to 2C" and examine the risks for 4C. Past policy documents have been described as being "very weak" by some observers.

A national response said: "Climate change is at the core of this government’s agenda, both building resilience and establishing itself as a low-carbon economy. It is essential that the UK is prepared for the effects."