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The direst potential impacts of the global heating for the UK have been detailed by researchers, encompassing a searing 4C jump in average temperatures to a 6.5-foot increase in sea levels. Another scenario envisions a decline of 6C in temperature following the shutdown of key Atlantic Ocean currents, which would massively disrupt farming and energy demand.

Plausible Events, Not Forecasts

These effects, some of which are linked to climate tipping points, are viewed as low probability but possible. The team explained that these models plugged a hole in risk assessment that had rendered the UK not ready for worst-case results.

"The worst-case scenarios we have mapped aren’t predictions, but they are possible," said Nigel Arnell who oversaw the research. "Britain has been planning without the methods to assess worst-case scenarios. We've now supplied planners what they need to get ready for future conditions they pray never occur, but can’t afford to ignore."

A Spectrum of Severe Conditions Projections

A further series of worst-case scenarios sets out the possible scale of harsh climate between now and the year 2100. These indicate that thermometer readings could skyrocket in certain periods by up to 6C above the norm, while rainfall could be 300% of typical amounts.

The probability of the extreme scenarios coming to pass cannot be precisely determined due to a lack of certainty about what action will be taken to tackle global warming and how the planet's climate will react. This research was likened to defence planning or scenario planning for financial systems.

Key Possibility Highlights

• Severe Heating: Global temperatures soaring past 4C by 2100 could happen if international cooperation fails or if powerful amplifying effects such as the Amazon basin dying emit its enormous store of carbon. This would cause extreme and prolonged heatwaves and droughts hitting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the North Atlantic current, is losing strength and becoming unstable due to global heating. A complete failure starting around 2030 would lead to a drastic cooling in the UK. "Agriculture would face immense difficulties and water supplies would be completely altered," explained Arnell.
• 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 collapse rapidly, submerging seaside communities. Differing from the other scenarios, this risk is already recognized by infrastructure experts.
• Clean Air Warming: Temperatures could also be driven up by about 0.75C if pollution from industry is rapidly cleaned up. This paradoxical outcome occurs because tiny specks from fossil fuel combustion scatter sunlight from reaching the ground.

Preparing for the Extreme

The severe models could be utilized in planning the development of critical national infrastructure, such as new towns, power generation facilities and urban drainage systems. Awareness of these future hazards could also hasten the push to reduce greenhouse gas emissions.

The research developed the extreme models using a combination of real-world events, climate models and established principles. The scenarios exclude broader worldwide issues such as the devastation of food supplies and increased conflict.

This work was initiated as part of a official climate resilience programme. Independent analyses have warned that insufficient focus was being given to catastrophic yet improbable risks.

An independent advisory body has stated that the UK must "prepare for two degrees of warming" and examine the risks for four degrees. Past policy documents have been labeled being "very weak" by certain experts.

A government spokesperson noted: "Global warming is at the core of this government’s agenda, both building resilience and becoming a clean energy superpower. It is vital that the UK is prepared for the consequences."