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The most severe possible consequences of the climate crisis for the UK have been outlined by researchers, encompassing a searing 4C jump in average temperatures to a two-metre increase in sea levels. An alternative projection envisions a decline of 6C in temperatures following the failure of key Atlantic Ocean currents, which would massively disrupt farming and energy demand.

Credible Events, Not Predictions

These impacts, a number of which are connected to climate tipping points, are considered as unlikely but plausible. The team explained that these models plugged a hole in risk assessment that had rendered the UK not ready for extreme outcomes.

"The climate extremes we have detailed are not forecasts, but they are plausible," commented the lead researcher who oversaw the analysis. "The nation has been making preparations in the absence of the frameworks to plan for worst-case scenarios. We've now provided policymakers what they need to get ready for future conditions they hope never happen, but can’t afford to ignore."

A Spectrum of Extreme Weather Scenarios

Another collection of worst-case scenarios maps the potential extent of severe conditions between now and the year 2100. These suggest that temperatures could rocket in some months by up to 6C above the norm, while precipitation could be triple standard measurements.

The likelihood of the worst-case outcomes occurring remains uncertain due to unknown factors about what steps will be taken to combat climate change and how the climate system will react. This research was described as similar to security threat evaluations or resilience checks for the banking sector.

Critical Scenario Highlights

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could transpire if international cooperation collapses or if powerful amplifying effects such as the Amazon basin dying release its vast reserves of carbon. This would lead to severe and lengthy heat domes and dry spells hitting the UK in summer.
• Ocean Circulation Failure: A key circulation system, the Atlantic meridional overturning circulation (Amoc), is slowing down and losing stability due to global heating. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would be severely challenged and freshwater availability would be completely altered," said the professor.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the polar regions collapse rapidly, submerging low-lying areas. Differing from the other scenarios, this threat is already known by infrastructure experts.
• Clean Air Warming: Global averages could also be driven up by about 0.75C if airborne particulates is sharply cut. This paradoxical outcome occurs because pollution particles from industrial activity reflect solar radiation from warming the ground.

Preparing for the Extreme

The severe models could be utilized in planning the building of long-term infrastructure, such as expanded cities, power generation facilities and urban drainage systems. Understanding these environmental threats could also hasten the drive to slash greenhouse gas emissions.

The research formulated the severe projections using a combination of real-world events, computer simulations and scientific theory. The possibilities do not take into account international cascading effects like the devastation of food supplies and increased conflict.

This work was requested as part of a official climate resilience programme. Earlier reports have warned that too little consideration was being allocated to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK must "prepare for two degrees of warming" and evaluate the dangers for 4C. Previous adaptation plans have been described as being "inadequate" by environmental groups.

An official statement said: "Global warming is at the heart of the country's focus, both preparing for impacts and transitioning to a renewable energy leader. It is essential that the UK is resilient for the impacts."