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The gravest possible consequences of the climate crisis for the UK have been mapped by scientists, encompassing a searing 4C increase in mean temperatures to a two-metre rise in ocean levels. An alternative projection predicts a drop of 6C in temperature following the collapse of key Atlantic Ocean currents, which would severely impact farming and power requirements.

Plausible Events, Not Forecasts

These consequences, some of which are connected to irreversible climate shifts, are seen as improbable but plausible. The team explained that these scenarios plugged a hole in forecasting that had left the UK ill-prepared for catastrophic possibilities.

"The climate extremes we have outlined aren’t predictions, but they are possible," commented the professor who directed the study. "The UK has been planning in the absence of the methods to test against extreme possibilities. We've now given planners what they need to get ready for climate outcomes they hope never happen, but must not overlook."

A Suite of Extreme Weather Possibilities

A second set of worst-case scenarios details the possible scale of extreme weather between now and the year 2100. These indicate that thermometer readings could soar in some months by up to 6C above average, while precipitation could be triple standard measurements.

The probability of the extreme scenarios occurring cannot be precisely determined due to uncertainty about what action will be implemented to tackle global warming and how the climate system will react. This approach was compared to security threat evaluations or resilience checks for financial systems.

Critical Scenario Highlights

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could happen if emissions cuts fails or if powerful amplifying effects including the Amazon basin becoming a net carbon source emit its huge repository of carbon. This would lead to intense and enduring heat domes and dry spells plaguing the UK in summer.
• Atlantic Current Collapse: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is slowing down and showing signs of collapse due to ocean warming. A collapse starting around 2030 would lead to a six-degree temperature drop in the UK. "Crop production would struggle enormously and water supplies would be completely altered," said the professor.
• Accelerated Coastal Flooding: A increase of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the polar regions disintegrate quickly, inundating coastal cities and towns. Unlike the other scenarios, this threat is already recognized by infrastructure experts.
• Aerosol Effect: Temperatures could also be driven up by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because tiny specks from industrial activity scatter solar radiation from warming the ground.

Preparing for the Extreme

These dire projections could be used to inform the building of major projects, including expanded cities, power generation facilities and urban drainage systems. Awareness of these climate risks could also accelerate the drive to slash fossil fuel emissions.

The research formulated the severe projections using a blend of past data and records, computer simulations and established principles. The possibilities exclude potential global problems such as the global food shortages and resource wars.

The research was commissioned as part of a national risk assessment framework. Earlier reports have warned that too little consideration was being given to low‐likelihood but high‐impact risks.

Official experts has stated that the UK must "prepare for two degrees of warming" and evaluate the threats for 4C. Past policy documents have been described as being "inadequate" by environmental groups.

A national response commented: "Climate change is at the heart of the country's focus, both building resilience and becoming a renewable energy leader. It is essential that the UK is ready for the effects."