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The direst projected effects of the climate crisis for the UK have been mapped by scientists, including a searing 4C jump in temperatures to a 2-metre surge in sea levels. Another scenario predicts a decline of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would profoundly upset farming and energy needs.

Possible Outcomes, Not Guarantees

These consequences, a number of which are linked to critical climate thresholds, are viewed as unlikely but plausible. The team explained that these scenarios filled a gap in planning that had rendered the UK not ready for catastrophic possibilities.

"The climate extremes we have mapped are not forecasts, but they are plausible," stated the lead researcher who led the study. "The UK has been planning without the tools to test against worst-case scenarios. We've now provided decision-makers what they need to plan for future conditions they pray never occur, but must not overlook."

A Range of Harsh Climate Possibilities

Another collection of worst-case scenarios sets out the potential extent of extreme weather between now and the end of the century. These suggest that thermometer readings could rocket in some months by up to 6C higher than average, while rainfall could be 300% of typical amounts.

The chance of the worst-case outcomes occurring cannot be precisely determined due to uncertainty about what steps will be implemented to combat climate change and how the climate system will respond. This approach was likened to national security risk assessments or stress tests for economic stability.

Critical Scenario Elements

• 4C Temperature Rise: Planetary heating soaring past 4C by 2100 could transpire if emissions cuts collapses or if strong feedback loops like the Amazon basin perishing unleash its enormous store of carbon. This would lead to intense and enduring heat domes and droughts plaguing the UK in summer.
• Atlantic Current Collapse: A critical sea current, the AMOC, is weakening and showing signs of collapse due to global heating. A collapse beginning in 2030 would lead to a drastic cooling in the UK. "Agriculture would struggle enormously and water supplies would be drastically changed," noted Arnell.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in the Arctic and Antarctic collapse rapidly, flooding coastal cities and towns. Differing from the other scenarios, this risk is already known by coastal engineers.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because tiny specks from burning coal reflect sunlight from reaching the ground.

Planning for the Unthinkable

The worst-case scenarios could be used to inform the development of critical national infrastructure, for example housing developments, nuclear power stations and flood defences. Knowledge about these climate risks could also accelerate the push to reduce fossil fuel emissions.

The study created the severe projections using a combination of real-world events, climate models and climate physics. These outcomes exclude international cascading effects including the devastation of food supplies and resource wars.

The research was initiated as part of a government’s risk assessment framework. Independent analyses have cautioned that too little consideration was being given to low‐likelihood but high‐impact risks.

The government's climate advisors has recommended that the UK needs to "prepare for two degrees of warming" and examine the risks for four degrees. Previous adaptation plans have been labeled being "very weak" by environmental groups.

An official statement noted: "Global warming is at the center of this government’s agenda, both adapting for the future and becoming a clean energy superpower. It is vital that the UK is ready for the consequences."