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The gravest projected effects of the global heating for the UK have been outlined by researchers, encompassing a blistering 4C increase in average temperatures to a 6.5-foot increase in sea level. An alternative projection predicts a plunge of 6C in temperatures following the shutdown of crucial Atlantic Ocean currents, which would severely impact farming and power requirements.

Possible Events, Not Predictions

These effects, some of which are associated with irreversible climate shifts, are considered as unlikely but plausible. The scientists explained that these projections plugged a hole in forecasting that had left the UK unprepared for worst-case results.

"The worst-case scenarios we have outlined are not forecasts, but they are plausible," commented the lead researcher who oversaw the analysis. "Britain has been planning lacking the tools to test against worst-case scenarios. We've now given decision-makers what they need to prepare for climate outcomes they hope never happen, but dare not dismiss."

A Suite of Severe Conditions Possibilities

A further series of worst-case scenarios sets out the projected severity of extreme weather between now and the year 2100. These suggest that temperatures could skyrocket in certain periods by up to 6C above average, while precipitation could be 300% of typical amounts.

The likelihood of the worst-case outcomes coming to pass could not be calculated due to a lack of certainty about what action will be implemented to address climate change and how the Earth's systems will react. This approach was likened to defence planning or scenario planning for financial systems.

Key Possibility Elements

• Severe Heating: Global temperatures soaring past 4C by 2100 could occur if international cooperation collapses or if powerful amplifying effects including the Amazon basin dying release its enormous store of carbon. This would lead to extreme and prolonged heatwaves and dry spells hitting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the AMOC, is losing strength and becoming unstable due to global heating. A full shutdown starting around 2030 would lead to a 6C cooling in the UK. "Agriculture would struggle enormously and water supplies would be completely altered," explained the lead researcher.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could happen if glaciers in the Arctic and Antarctic disintegrate quickly, submerging coastal cities and towns. Unlike the other scenarios, this threat is already understood by infrastructure experts.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if pollution from industry is sharply cut. This unexpected result occurs because tiny specks from industrial activity reflect solar radiation from warming the ground.

Preparing for the Extreme

The severe models could be applied to guide the building of major projects, such as expanded cities, nuclear power stations and urban drainage systems. Knowledge about these climate risks could also hasten the drive to reduce carbon pollution.

The analysis developed the extreme models using a mix of observed and historical experience, climate models and climate physics. The possibilities omit broader worldwide issues including the devastation of food supplies and geopolitical instability.

This work was initiated as part of a official climate resilience programme. Earlier reports have cautioned that not enough attention was being given to high-consequence, low-probability risks.

The government's climate advisors has said that the UK needs to "become resilient to moderate heating" and assess the threats for four degrees. Previous adaptation plans have been labeled being "insufficient" by certain experts.

A government spokesperson noted: "The climate emergency is at the heart of our national priorities, both preparing for impacts and transitioning to a low-carbon economy. It is essential that the UK is ready for the consequences."