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The gravest potential impacts of the climate crisis for the UK have been mapped by scientists, encompassing a scorching 4C jump in mean temperatures to a two-metre surge in ocean levels. A separate possibility envisions a plunge of 6C in temperatures following the collapse of crucial Atlantic Ocean currents, which would severely impact farming and power requirements.

Possible Events, Not Predictions

These effects, some of which are associated with critical climate thresholds, are seen as low probability but plausible. The team explained that these models plugged a hole in forecasting that had left the UK ill-prepared for catastrophic possibilities.

"The worst-case scenarios we have mapped are not forecasts, but they are plausible," said Nigel Arnell who led the analysis. "Britain has been making preparations in the absence of the tools to assess extreme possibilities. We've now given planners what they need to plan for future conditions they hope never happen, but can’t afford to ignore."

A Spectrum of Harsh Climate Possibilities

A second set of severe models maps the projected severity of harsh climate between now and the end of the century. These indicate that temperatures could skyrocket in some months by up to 6C above historical levels, while precipitation could be 300% of standard measurements.

The likelihood of the worst-case outcomes occurring cannot be precisely determined due to uncertainty about what action will be enacted to tackle global warming and how the planet's climate will respond. This analysis was described as similar to security threat evaluations or resilience checks for the banking sector.

Key Scenario Highlights

• 4C Temperature Rise: Worldwide averages rising well above 4C by 2100 could transpire if climate action collapses or if powerful amplifying effects such as the Amazon rainforest dying unleash its huge repository of carbon. This would cause severe and lengthy heat domes and droughts hitting the UK in summer.
• Atlantic Current Collapse: A critical sea current, the Atlantic meridional overturning circulation (Amoc), is weakening and showing signs of collapse due to ocean warming. A collapse beginning in 2030 would lead to a six-degree temperature drop in the UK. "Crop production would struggle enormously and freshwater availability would be completely altered," said the lead researcher.
• Rapid Sea Level Rise: A surge of 2.0-2.2 metres around the UK by 2100 could take place if ice sheets in Greenland and Antarctica disintegrate quickly, submerging seaside communities. Differing from the other scenarios, this risk is already recognized by infrastructure experts.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if pollution from industry is rapidly cleaned up. This counterintuitive effect occurs because pollution particles from industrial activity block sunlight from warming the ground.

Preparing for the Unthinkable

The worst-case scenarios could be utilized in planning the building of major projects, such as housing developments, energy plants and urban drainage systems. Knowledge about these environmental threats could also accelerate the push to cut fossil fuel emissions.

The study developed the worst-case scenarios using a combination of real-world events, digital projections and established principles. These outcomes do not take into account broader worldwide issues including the devastation of food supplies and increased conflict.

The project was requested as part of a national climate resilience programme. Independent analyses have warned that not enough attention was being allocated to low‐likelihood but high‐impact risks.

The government's climate advisors has said that the UK must "adapt to 2C" and examine the risks for 4C. Earlier government strategies have been labeled being "very weak" by environmental groups.

A national response commented: "Climate change is at the core of our national priorities, both building resilience and transitioning to a clean energy superpower. It is crucial that the UK is resilient for the effects."