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The gravest potential impacts of the climate crisis for the UK have been mapped by scientists, ranging from a searing 4C rise in mean temperatures to a two-metre surge in sea levels. Another scenario envisions a drop of 6C in temperature following the shutdown of critical Atlantic Ocean currents, which would profoundly upset agriculture and energy demand.

Plausible Outcomes, Not Guarantees

These effects, a number of which are connected to critical climate thresholds, are considered as improbable but plausible. The team explained that these projections addressed a shortfall in planning that had left the UK unprepared for extreme outcomes.

"The worst-case scenarios we have detailed aren’t predictions, but they are credible," commented the lead researcher who led the study. "The nation has been making preparations lacking the methods to assess worst-case scenarios. We've now supplied planners what they need to prepare for future conditions they hope never happen, but must not overlook."

A Range of Extreme Weather Scenarios

Another collection of severe models maps the projected severity of severe conditions between now and the year 2100. These suggest that thermometer readings could skyrocket in particular seasons by up to 6C above historical levels, while rainfall could be 300% of normal levels.

The chance of the extreme scenarios occurring remains uncertain due to uncertainty about what steps will be enacted to tackle global warming and how the planet's climate will behave. This analysis was compared to defence planning or scenario planning for economic stability.

Key Scenario Elements

• 4C Temperature Rise: Global temperatures soaring past 4C by 2100 could happen if emissions cuts fails or if strong feedback loops including the tropical forests dying emit its huge repository of carbon. This would cause intense and enduring heatwaves and dry spells affecting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the North Atlantic current, is losing strength and becoming unstable due to global heating. A collapse starting around 2030 would lead to a six-degree temperature drop in the UK. "Crop production would be severely challenged and water supplies would be completely altered," noted Arnell.
• Accelerated Coastal Flooding: A rise of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic collapse rapidly, submerging coastal cities and towns. Differing from the other scenarios, this risk is already recognized by planners.
• Pollution Paradox: Temperatures could also be increased by about 0.75C if pollution from industry is sharply cut. This unexpected result occurs because aerosol particles from industrial activity scatter sunlight from reaching the ground.

Planning for the Extreme

The worst-case scenarios could be utilized in planning the development of long-term infrastructure, including expanded cities, nuclear power stations and flood defences. Knowledge about these environmental threats could also hasten the push to cut fossil fuel emissions.

The analysis developed the worst-case scenarios using a mix of past data and records, climate models and climate physics. These outcomes exclude potential global problems including the agricultural collapse and increased conflict.

The research was commissioned as part of a government’s climate resilience programme. Earlier reports have warned that not enough attention was being given to low‐likelihood but high‐impact risks.

An independent advisory body has said that the UK must "adapt to 2C" and examine the risks for four degrees. Previous adaptation plans have been labeled being "insufficient" by some observers.

A national response said: "The climate emergency is at the heart of our national priorities, both adapting for the future and transitioning to a clean energy superpower. It is vital that the UK is prepared for the effects."