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The gravest projected effects of the climate crisis for the UK have been outlined by scientists, encompassing a blistering 4C increase in average temperatures to a two-metre surge in sea levels. An alternative projection foresees a drop of 6C in temperatures following the collapse of key Atlantic Ocean currents, which would severely impact agriculture and power requirements.

Credible Extremes, Not Forecasts

These effects, some of which are linked to irreversible climate shifts, are seen as unlikely but credible. The scientists explained that these models addressed a shortfall in forecasting that had left the UK not ready for extreme outcomes.

"The climate extremes we have outlined aren’t predictions, but they are credible," said Nigel Arnell who led the study. "The nation has been formulating policy lacking the methods to assess worst-case scenarios. We've now given policymakers what they need to plan for climate outcomes they wish to avoid, but can’t afford to ignore."

A Range of Extreme Weather Scenarios

A further series of dire projections sets out the potential extent of harsh climate between now and the year 2100. These show that temperatures could soar in some months by up to 6C above historical levels, while precipitation could be triple standard measurements.

The probability of the worst-case outcomes coming to pass remains uncertain due to unknown factors about what measures will be implemented to address global heating and how the climate system will react. This approach was compared to security threat evaluations or scenario planning for economic stability.

Key Scenario Details

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could happen if international cooperation fails or if strong feedback loops like the Amazon rainforest becoming a net carbon source release its huge repository of carbon. This would result in extreme and prolonged heat domes and water shortages hitting the UK in summer.
• Atlantic Current Collapse: A major ocean current, the AMOC, is weakening and losing stability due to global heating. A full shutdown commencing by 2030 would lead to a 6C cooling in the UK. "Farming would face immense difficulties and water resources would be completely altered," noted the professor.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could happen if polar ice in the polar regions collapse rapidly, flooding seaside communities. Unlike the other scenarios, this possibility is already recognized by planners.
• Pollution Paradox: Global averages could also be pushed higher by about 0.75C if pollution from industry is sharply cut. This unexpected result occurs because tiny specks from fossil fuel combustion block sunlight from reaching the ground.

Planning for the Unthinkable

The worst-case scenarios could be utilized in planning the construction of long-term infrastructure, for example housing developments, power generation facilities and water management networks. Awareness of these climate risks could also accelerate the transition to slash greenhouse gas emissions.

The research developed the extreme models using a combination of observed and historical experience, computer simulations and climate physics. The possibilities omit international cascading effects including the global food shortages and resource wars.

The research was requested as part of a government’s risk assessment framework. Previous assessments have stated that insufficient focus was being allocated to low‐likelihood but high‐impact risks.

Official experts has said that the UK needs to "adapt to 2C" and evaluate the dangers for severe warming. Past policy documents have been labeled being "inadequate" by environmental groups.

A government spokesperson noted: "The climate emergency is at the center of our national priorities, both adapting for the future and becoming a low-carbon economy. It is crucial that the UK is ready for the impacts."