New climate models suggest that global temperatures could rise by 3.5°C (6.3°F) by 2100 if current climate policies fail, according to a recent study. This "high-emissions scenario" predicts severe impacts, including strong sea level rises, more extreme weather events, and significant effects on crop yields. Lead author Professor Detlef van Vuuren from the University of Utrecht warns that this scenario could trigger major impacts on key ocean currents such as the Atlantic Meridional Overturning Circulation (AMOC).

The Science Behind the Scenarios

The newly defined "high-emissions scenario" is part of the Scenario Model Intercomparison Project (ScenarioMIP), an international effort involving 20 scientific experts. These scenarios are used to predict future climate outcomes based on different policy actions. The models will also form the basis for the next major assessment by the UN's Intergovernmental Panel on Climate Change (IPCC), which will guide global environmental policy .

According to the report,the high-emissions scenario would require a significant expansion of fossil fuel use and a decline in renewable energy adoption. This scenario is not a "business-as-usual" situation but would involve active opposition to climate action, such as resistance to building new wind farms or concerns about employment in fossil fuel industries.

Comparing Worst-Case Scenarios

The current worst-case scenario predicts a 3.5°C temperature rise by 2100, which is significantly cooler than the previous prediction of 4.5°C by 2100. However,the new models suggest that 4.5°C warming is still plausible but has been pushed back to 2130. This change is attributed to the lower costs of renewables compared to fossil fuels and some emerging impacts of climate policy.

Despite the updated predictions, there remains uncertainty about the exact outcome of the worst-case scenario.. if the climate is more sensitive to greenhouse gases than predicted, the temperature rise could be closer to 4°C (7.2°F) by 2100.

Preparing for the Worst

Professor van Vuuren emphasizes the importance of preparing for the worst possible outcomes.. Governments need to build robust defenses against extreme climate events, such as flood defenses in the UK and dikes in the Netherlands. He notes that "in most things in life, we make sure that we build in safety," highlighting the need for proactive measures to mitigate climate impacts.

According to the report, the last 11 years have been the hottest on record, indicating that Earth's climate is more out of balance than ever before. The new models aim to help societies plan for and adapt to these changes, ensuring that they are prepared for the most extreme scenarios.

Unanswered Questions and Uncertainties

The study raises several unanswered questions and uncertainties. One key question is whether the climate is more sensitive to greenhouse gases than current models predict. Additionally , the report does not address the potential for unexpected geopolitical factors or local issues that could exacerbate climate change.

Another uncertainty is the impact of opposition to renewable energy projects and concerns about employment in fossil fuel industries. The report also does not provide a clear timeline for when the worst-case scenario might occur, leaving open the possibility of even more severe climate impacts in the future.