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The most severe possible consequences of the climate crisis for the UK have been detailed by scientists, including a searing 4C jump in mean temperatures to a 2-metre surge in ocean levels. Another scenario envisions a plunge of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would severely impact agriculture and energy needs.

Credible Outcomes, Not Guarantees

These effects, some of which are associated with critical climate thresholds, are seen as low probability but credible. The team said that these scenarios addressed a shortfall in risk assessment that had left the UK unprepared for catastrophic possibilities.

"The severe weather events we have mapped are not forecasts, but they are credible," stated the lead researcher who directed the research. "The nation has been planning lacking the tools to test against worst-case scenarios. We've now given decision-makers what they need to plan for climate outcomes they hope never happen, but dare not dismiss."

A Range of Severe Conditions Possibilities

Another collection of worst-case scenarios details the projected severity of extreme weather between now and the close of the 2100s. These indicate that temperatures could soar in some months by up to 6C above historical levels, while rainfall could be 300% of standard measurements.

The chance of the worst-case outcomes occurring cannot be precisely determined due to unknown factors about what measures will be implemented to address global heating and how the climate system will respond. This research was described as similar to national security risk assessments or stress tests for the banking sector.

Major Outcome Elements

• Severe Heating: Global temperatures rising well above 4C by 2100 could occur if international cooperation collapses or if vicious cycles including the Amazon basin perishing emit its huge repository of carbon. This would cause severe and lengthy heat domes and dry spells affecting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is losing strength and losing stability due to ocean warming. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and freshwater availability would be fundamentally reshaped," said Arnell.
• Sudden Ocean Inundation: A rise of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic melt abruptly, inundating seaside communities. In contrast to the other scenarios, this threat is already recognized by coastal engineers.
• Pollution Paradox: Temperatures could also be pushed higher by about 0.75C if pollution from industry is drastically reduced. This unexpected result occurs because pollution particles from industrial activity block sunlight from warming the ground.

Preparing for the Worst

These dire projections could be utilized in planning the development of long-term infrastructure, including housing developments, energy plants and urban drainage systems. Knowledge about these climate risks could also hasten the transition to reduce carbon pollution.

The research formulated the severe projections using a combination of real-world events, computer simulations and climate physics. These outcomes exclude international cascading effects such as the devastation of food supplies and geopolitical instability.

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

Official experts has said that the UK needs to "adapt to 2C" and evaluate the threats for severe warming. Previous adaptation plans have been criticised as being "insufficient" by some observers.

An official statement noted: "Climate change is at the heart of our national priorities, both building resilience and transitioning to a low-carbon economy. It is crucial that the UK is resilient for the impacts."