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The most severe potential impacts of the global heating for the UK have been outlined by researchers, encompassing a searing 4C rise in mean temperatures to a two-metre surge in sea level. An alternative projection foresees a plunge of 6C in temperature following the failure of key Atlantic Ocean currents, which would profoundly upset agriculture and energy needs.

Possible Events, Not Predictions

These impacts, a number of which are associated with critical climate thresholds, are considered as low probability but plausible. The researchers explained that these models addressed a shortfall in planning that had left the UK ill-prepared for worst-case results.

"The severe weather events we have detailed should not be seen as certainties, but they are plausible," stated the professor who oversaw the analysis. "The nation has been making preparations without the frameworks to test against catastrophic outcomes. We've now provided decision-makers what they need to plan for future conditions they pray never occur, but must not overlook."

A Spectrum of Extreme Weather Projections

A further series of worst-case scenarios sets out the possible scale of harsh climate between now and the close of the 2100s. These indicate that temperatures could skyrocket in particular seasons by up to 6C higher than the norm, while precipitation could be three times typical amounts.

The probability of the extreme scenarios occurring could not be calculated due to unknown factors about what measures will be implemented to combat global warming and how the climate system will respond. This research was likened to national security risk assessments or stress tests for economic stability.

Major Outcome Details

• 4C Temperature Rise: Worldwide averages exceeding 4C by 2100 could transpire if international cooperation collapses or if strong feedback loops such as the Amazon basin becoming a net carbon source emit its enormous store of carbon. This would cause extreme and prolonged heatwaves and dry spells affecting the UK in summer.
• Ocean Circulation Failure: A major ocean current, the AMOC, is slowing down and losing stability due to global heating. A collapse starting around 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and water supplies would be completely altered," explained Arnell.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in Greenland and Antarctica disintegrate quickly, flooding seaside communities. Unlike the other scenarios, this threat is already known by infrastructure experts.
• Pollution Paradox: Temperatures could also be driven up by about 0.75C if airborne particulates is drastically reduced. This counterintuitive effect occurs because tiny specks from industrial activity reflect solar radiation from reaching the ground.

Preparing for the Worst

The worst-case scenarios could be applied to guide the development of long-term infrastructure, for example new towns, nuclear power stations and water management networks. Awareness of these future hazards could also speed the push to slash greenhouse gas emissions.

The study created the extreme models using a mix of real-world events, climate models and established principles. These outcomes do not take into account international cascading effects such as the global food shortages and geopolitical instability.

The research was requested as part of a national risk assessment framework. Previous assessments have stated that not enough attention was being paid to catastrophic yet improbable risks.

Official experts has recommended that the UK needs to "become resilient to moderate heating" and evaluate the threats for four degrees. Previous adaptation plans have been criticised as being "very weak" by certain experts.

A national response noted: "Climate change is at the core of our national priorities, both adapting for the future and transitioning to a low-carbon economy. It is vital that the UK is resilient for the effects."