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Sensitivity of the ECMWF seasonal forecast model to CO2 and anthropogenic aerosol forcings: Experimental design and impact on climate trends

Michael Mayer, Daniel J. Befort, Jacob Maddison, Antje Weisheimer

Featured August 25, 2026

Original Paper

AI-generated analysis — This is SciGrove's AI interpretation of the paper, not peer-reviewed content. Always refer to the original paper.

Simply

Scientists created special "what-if" climate forecasts by changing pollution levels and adjusting the ocean's starting warmth, showing how human activities drive climate trends while revealing a model weakness in tropical ocean-atmosphere interactions.

In depth
The paper introduces a novel framework of counterfactual seasonal hindcasts to investigate the sensitivity of climate trends to anthropogenic forcings. This involves modifying atmospheric CO₂ and aerosol forcings, and crucially, adjusting ocean and sea-ice initial conditions based on observation-derived forced signals, allowing for a more dynamically consistent assessment of climate change impacts on decadal trends while preserving seasonal prediction skill.

Key Takeaways

  • 1
    The study develops a novel framework of counterfactual seasonal hindcasts by perturbing both atmospheric forcings and observation-based ocean/sea-ice initial conditions.
  • 2
    This approach allows for a dynamically consistent assessment of anthropogenic forcing impacts on climate trends, demonstrating that altered ocean initial conditions are key to reproducing observed decadal trends.
  • 3
    The experiments reveal a fundamental model limitation: the coupled atmosphere-ocean system struggles to sustain enhanced tropical Pacific SST gradients through Bjerknes feedbacks, indicating weak atmospheric sensitivity.

Conceptual Flow

HIGH LEVEL
1
Simulating "What If" Climate Scenarios

They ran many climate forecasts starting from real conditions but pretending pollution was different, to see how the climate would have changed.

Real Climate Start
Different Pollution Levels
Run Forecasts
Possible Future Climates
2
Uncovering Climate Drivers and Model Limits

These "what-if" forecasts showed that human pollution strongly changes long-term warming, but the model struggles to keep tropical ocean temperatures accurate.

Pollution Changes
Ocean Start Adjustments
Reveal Climate Trends
Stronger Warming
Model Weakness Found

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