Climate models have long suggested that human-caused greenhouse gas emissions will likely lead to drier conditions in Europe, especially in spring and summer. However, different climate models do not agree on how strong or how fast this drying will be. Some models show large changes, while others show much smaller ones.

To understand why these models differ, scientists have studied several possible causes. These include the effects of air pollution particles (called aerosols), changes in large-scale weather patterns, and feedbacks from the land surface.

In this study, we examine these processes in more detail. We first analyze them using a single atmospheric model, and then compare results across two groups of climate models that include both the ocean and the atmosphere. Overall, our findings are similar to earlier studies, but we identify a serious and policy-relevant problem: climate models do not match real-world observations well over the past few decades (from 1979 to 2022).

This mismatch does not appear to be caused by errors in how models simulate weather patterns and their year-to-year variations. Instead, it is most likely linked to systematic errors in how models represent the cooling effects of sulfate aerosols, a type of air pollution.

Using a statistical approach that combines model results with observations, we adjust the latest climate projections. This analysis suggests that Western Europe may dry faster than previously expected. Our results also raise important questions about how aerosol effects are calibrated in climate models and the relevance of global warming levels for reducing uncertainties in climate projections.