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The most severe possible consequences of the global heating for the UK have been outlined by scientists, encompassing a blistering 4C rise in temperatures to a 6.5-foot surge in sea level. An alternative projection predicts a drop of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would massively disrupt food production and energy demand.

Credible Outcomes, Not Predictions

These impacts, a number of which are linked to irreversible climate shifts, are considered as unlikely but credible. The team stated that these scenarios filled a gap in forecasting that had left the UK not ready for worst-case results.

"The severe weather events we have detailed are not forecasts, but they are credible," commented the lead researcher who oversaw the research. "The UK has been making preparations in the absence of the frameworks to plan for catastrophic outcomes. We've now provided decision-makers what they need to plan for environmental results they wish to avoid, but dare not dismiss."

A Spectrum of Severe Conditions Scenarios

Another collection of dire projections details the potential extent of extreme weather between now and the end of the century. These indicate that temperatures could rocket in some months by up to 6C above the norm, while rainfall could be 300% of normal levels.

The chance of the extreme scenarios coming to pass remains uncertain due to a lack of certainty about what measures will be implemented to address climate change and how the Earth's systems will react. This analysis was described as similar to national security risk assessments or resilience checks for economic stability.

Key Outcome Highlights

• 4C Temperature Rise: Global temperatures soaring past 4C by 2100 could occur if international cooperation collapses or if vicious cycles including the Amazon rainforest dying unleash its vast reserves of carbon. This would lead to severe and lengthy heatwaves and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the Atlantic meridional overturning circulation (Amoc), is weakening and losing stability due to global heating. A full shutdown beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would struggle enormously and freshwater availability would be completely altered," said the lead researcher.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the polar regions disintegrate quickly, submerging coastal cities and towns. In contrast to the other scenarios, this risk is already understood by infrastructure experts.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if airborne particulates is drastically reduced. This paradoxical outcome occurs because aerosol particles from industrial activity block sunlight from warming the ground.

Building Resilience Against the Worst

These dire projections could be used to inform the construction of critical national infrastructure, including new towns, energy plants and urban drainage systems. Knowledge about these environmental threats could also accelerate the transition to cut greenhouse gas emissions.

The research created the worst-case scenarios using a blend of past data and records, computer simulations and climate physics. The possibilities do not take into account international cascading effects like the agricultural collapse and geopolitical instability.

The research was commissioned as part of a government’s climate resilience programme. Earlier reports have warned that not enough attention was being paid to catastrophic yet improbable risks.

The government's climate advisors has said that the UK needs to "become resilient to moderate heating" and evaluate the dangers for four degrees. Previous adaptation plans have been criticised as being "inadequate" by some observers.

A national response noted: "Climate change is at the center of the country's focus, both adapting for the future and becoming a clean energy superpower. It is essential that the UK is ready for the impacts."