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The gravest projected effects of the climate emergency for the UK have been detailed by researchers, encompassing a blistering 4C increase in average temperatures to a two-metre rise in ocean levels. An alternative projection predicts a drop of 6C in temperature following the shutdown of crucial Atlantic Ocean currents, which would massively disrupt agriculture and energy demand.

Credible Events, Not Guarantees

These impacts, a number of which are associated with irreversible climate shifts, are considered as low probability but plausible. The team explained that these scenarios filled a gap in forecasting that had rendered the UK unprepared for catastrophic possibilities.

"The worst-case scenarios we have outlined should not be seen as certainties, but they are possible," said the lead researcher who directed the study. "The UK has been formulating policy in the absence of the frameworks to test against catastrophic outcomes. We've now given policymakers what they need to prepare for climate outcomes they hope never happen, but must not overlook."

A Range of Extreme Weather Scenarios

Another collection of worst-case scenarios maps the projected severity of extreme weather between now and the close of the 2100s. These suggest that temperatures could skyrocket in particular seasons by up to 6C above historical levels, while precipitation could be three times standard measurements.

The probability of the catastrophic events happening remains uncertain due to unknown factors about what action will be taken to combat global heating and how the Earth's systems will react. This research was described as similar to national security risk assessments or resilience checks for financial systems.

Key Outcome Elements

• 4C Temperature Rise: Planetary heating exceeding 4C by 2100 could transpire if international cooperation fails or if vicious cycles like the Amazon rainforest dying release its huge repository of carbon. This would cause intense and enduring heat domes and water shortages hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the AMOC, is slowing down and becoming unstable due to global heating. A full shutdown beginning in 2030 would lead to a six-degree temperature drop in the UK. "Crop production would face immense difficulties and freshwater availability would be completely altered," noted Arnell.
• Accelerated Coastal Flooding: A surge of 2.0-2.2 metres around the UK by 2100 could take place if polar ice in Greenland and Antarctica melt abruptly, submerging low-lying areas. In contrast to the other scenarios, this threat is already understood by infrastructure experts.
• Aerosol Effect: Temperatures could also be pushed higher by about 0.75C if airborne particulates is drastically reduced. This unexpected result occurs because pollution particles from burning coal scatter solar radiation from warming the ground.

Preparing for the Extreme

These dire projections could be used to inform the building of long-term infrastructure, such as housing developments, power generation facilities and urban drainage systems. Understanding these future hazards could also speed the drive to slash greenhouse gas emissions.

The research developed the severe projections using a mix of observed and historical experience, computer simulations and established principles. The scenarios do not take into account broader worldwide issues such as the devastation of food supplies and increased conflict.

The project was initiated as part of a government’s risk assessment framework. Independent analyses have warned that too little consideration was being paid to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK must "adapt to 2C" and evaluate the risks for 4C. Previous adaptation plans have been labeled being "very weak" by certain experts.

An official statement said: "The climate emergency is at the center of this government’s agenda, both preparing for impacts and transitioning to a clean energy superpower. It is crucial that the UK is ready for the consequences."