European amphibians and birds have been breeding consistently earlier over the past two to three decades1,2. These changes have been attributed to the observed trends in increasing average spring temperatures in Europe3 producing earlier growing seasons4 and increased forage availability. Here we show that variations in breeding of European amphibians and birds are influenced by variations in a natural, large-scale atmospheric phenomenon, the North Atlantic Oscillation (NAO). Our results support the proximate cause (that is, increase in spring temperatures) of the altered breeding phenology as suggested previously1,2, but by extending previous analyses as well as integrating data from other bird species, they also suggest that organisms with complex life histories respond to year-to-year variations in their abiotic environment.