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The gravest projected effects of the global heating for the UK have been outlined by experts, including a searing 4C rise in temperatures to a 6.5-foot increase in ocean levels. Another scenario predicts a decline of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would severely impact agriculture and energy demand.

Credible Outcomes, Not Predictions

These consequences, some of which are associated with critical climate thresholds, are seen as low probability but plausible. The team stated that these models filled a gap in forecasting that had left the UK not ready for worst-case results.

"The severe weather events we have outlined aren’t predictions, but they are credible," commented the professor who led the study. "The nation has been formulating policy lacking the frameworks to plan for worst-case scenarios. We've now provided planners what they need to plan for future conditions they hope never happen, but can’t afford to ignore."

A Spectrum of Severe Conditions Possibilities

Another collection of dire projections maps the potential extent of harsh climate between now and the year 2100. These show that temperatures could rocket in certain periods by up to 6C higher than the norm, while rainfall could be three times standard measurements.

The probability of the worst-case outcomes occurring remains uncertain due to unknown factors about what steps will be implemented to tackle global heating and how the Earth's systems will respond. This research was likened to security threat evaluations or scenario planning for financial systems.

Major Outcome Details

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could transpire if climate action collapses or if vicious cycles like the Amazon basin dying emit its vast reserves of carbon. This would result in intense and enduring heatwaves and droughts hitting the UK in summer.
• AMOC Shutdown: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is weakening and showing signs of collapse due to ocean warming. A full shutdown commencing by 2030 would lead to a 6C cooling in the UK. "Farming would face immense difficulties and freshwater availability would be fundamentally reshaped," noted the professor.
• Sudden Ocean Inundation: A surge of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in Greenland and Antarctica disintegrate quickly, submerging coastal cities and towns. In contrast to the other scenarios, this possibility is already understood by planners.
• Clean Air Warming: Global averages could also be pushed higher by about 0.75C if airborne particulates is sharply cut. This unexpected result occurs because aerosol particles from burning coal scatter solar radiation from reaching the ground.

Preparing for the Unthinkable

The worst-case scenarios could be applied to guide the building of major projects, for example expanded cities, power generation facilities and water management networks. Understanding these environmental threats could also speed the drive to reduce carbon pollution.

The research created the worst-case scenarios using a mix of observed and historical experience, computer simulations and climate physics. These outcomes exclude international cascading effects like the agricultural collapse and geopolitical instability.

The project was initiated as part of a national adaptation planning initiative. Previous assessments have warned that not enough attention was being given to low‐likelihood but high‐impact risks.

Official experts has said that the UK needs to "prepare for two degrees of warming" and assess the threats for four degrees. Earlier government strategies have been criticised as being "insufficient" by certain experts.

An official statement said: "Climate change is at the heart of this government’s agenda, both adapting for the future and establishing itself as a renewable energy leader. It is vital that the UK is prepared for the effects."