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The gravest potential impacts of the global heating for the UK have been outlined by researchers, encompassing a scorching 4C jump in average temperatures to a 6.5-foot rise in ocean levels. Another scenario envisions a decline of 6C in temperatures following the shutdown of key Atlantic Ocean currents, which would severely impact farming and power requirements.

Plausible Events, Not Guarantees

These effects, some of which are associated with critical climate thresholds, are seen as low probability but possible. The scientists explained that these scenarios plugged a hole in risk assessment that had rendered the UK unprepared for extreme outcomes.

"The severe weather events we have mapped aren’t predictions, but they are plausible," said the professor who directed the research. "The nation has been planning in the absence of the tools to test against catastrophic outcomes. We've now provided policymakers what they need to prepare for future conditions they wish to avoid, but must not overlook."

A Spectrum of Extreme Weather Projections

A further series of worst-case scenarios details the projected severity of extreme weather between now and the end of the century. These indicate that thermometer readings could rocket in particular seasons by up to 6C higher than the norm, while precipitation could be 300% of typical amounts.

The probability of the extreme scenarios happening could not be calculated due to unknown factors about what measures will be taken to address climate change and how the planet's climate will behave. This analysis was likened to security threat evaluations or stress tests for financial systems.

Critical Scenario Highlights

• Four-Degree Warming: Planetary heating soaring past 4C by 2100 could transpire if international cooperation collapses or if vicious cycles including the tropical forests perishing unleash its vast reserves of carbon. This would result in extreme and prolonged heat domes and droughts affecting the UK in summer.
• AMOC Shutdown: A critical sea current, the AMOC, is losing strength and showing signs of collapse due to climate change. A full shutdown starting around 2030 would lead to a six-degree temperature drop in the UK. "Agriculture would face immense difficulties and water supplies would be drastically changed," said Arnell.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could occur if polar ice in the Arctic and Antarctic melt abruptly, submerging seaside communities. Differing from the other scenarios, this threat is already known by coastal engineers.
• Aerosol Effect: Temperatures could also be increased by about 0.75C if airborne particulates is drastically reduced. This paradoxical outcome occurs because tiny specks from fossil fuel combustion reflect solar radiation from warming the ground.

Preparing for the Worst

The severe models could be applied to guide the building of long-term infrastructure, such as expanded cities, energy plants and water management networks. Understanding these climate risks could also accelerate the transition to slash fossil fuel emissions.

The study created the extreme models using a combination of past data and records, climate models and climate physics. These outcomes exclude broader worldwide issues such as the global food shortages and geopolitical instability.

The research was requested as part of a government’s climate resilience programme. Previous assessments have warned that not enough attention was being given to catastrophic yet improbable risks.

The government's climate advisors has recommended that the UK must "prepare for two degrees of warming" and evaluate the threats for severe warming. Earlier government strategies have been described as being "inadequate" by certain experts.

An official statement noted: "The climate emergency is at the center of our national priorities, both building resilience and establishing itself as a renewable energy leader. It is essential that the UK is ready for the consequences."