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The gravest possible consequences of the climate emergency for the UK have been detailed by scientists, encompassing a scorching 4C rise in average temperatures to a two-metre rise in sea level. An alternative projection foresees a decline of 6C in temperature following the collapse of key Atlantic Ocean currents, which would profoundly upset agriculture and energy needs.

Possible Outcomes, Not Forecasts

These consequences, certain ones are connected to irreversible climate shifts, are considered as improbable but credible. The team said that these projections addressed a shortfall in forecasting that had rendered the UK not ready for extreme outcomes.

"The climate extremes we have outlined should not be seen as certainties, but they are credible," said Nigel Arnell who directed the study. "The nation has been formulating policy in the absence of the methods to plan for worst-case scenarios. We've now given policymakers what they need to get ready for future conditions they hope never happen, but can’t afford to ignore."

A Suite of Extreme Weather Possibilities

A further series of severe models maps the possible scale of severe conditions between now and the year 2100. These show that thermometer readings could skyrocket in particular seasons by up to 6C above historical levels, while precipitation could be 300% of typical amounts.

The chance of the catastrophic events occurring remains uncertain due to uncertainty about what steps will be implemented to address climate change and how the climate system will behave. This research was likened to security threat evaluations or scenario planning for financial systems.

Key Scenario Highlights

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could happen if climate action collapses or if strong feedback loops including the Amazon basin becoming a net carbon source release its vast reserves of carbon. This would lead to extreme and prolonged heat domes and droughts hitting the UK in summer.
• Ocean Circulation Failure: A critical sea current, the North Atlantic current, is losing strength and losing stability due to ocean warming. A collapse starting around 2030 would lead to a 6C cooling in the UK. "Crop production would face immense difficulties and water resources would be fundamentally reshaped," explained Arnell.
• Sudden Ocean Inundation: A increase of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the polar regions collapse rapidly, inundating low-lying areas. Unlike the other scenarios, this possibility is already known by coastal engineers.
• Clean Air Warming: Global averages could also be increased by about 0.75C if pollution from industry is drastically reduced. This unexpected result occurs because aerosol particles from fossil fuel combustion reflect sunlight from reaching the ground.

Preparing for the Extreme

These dire projections could be applied to guide the construction of major projects, such as new towns, energy plants and flood defences. Understanding these future hazards could also speed the push to cut fossil fuel emissions.

The study created the severe projections using a combination of observed and historical experience, digital projections and scientific theory. These outcomes do not take into account international cascading effects such as the agricultural collapse and resource wars.

This work was requested as part of a government’s risk assessment framework. Independent analyses have stated that insufficient focus was being paid to catastrophic yet improbable risks.

An independent advisory body has recommended that the UK needs to "adapt to 2C" and evaluate the dangers for severe warming. Past policy documents have been criticised as being "insufficient" by some observers.

An official statement noted: "Global warming is at the core of this government’s agenda, both adapting for the future and transitioning to a clean energy superpower. It is essential that the UK is prepared for the consequences."