While the effects of global atmospheric changes on vegetation and resulting insect populations(‘bottom-up interactions’) are being increasingly studied, how these gases modify interactions among insects and their natural enemies (‘top-down interactions’) is less clear. As natural enemy efficacy is governed largely by behavioural mechanisms, altered prey finding and prey defence may change insect population dynamics. Here we show that pheromone-mediated escape behaviours, and hence the vulnerability of insects to natural enemies, are divergent under atmospheric conditions associated with global climate change. Chaitophorus stevensis, a common aphid on trembling aspen trees, Populus tremuloides, have diminished escape responses in enriched carbon dioxide (CO2) environments, while those in enriched ozone (O3) have augmented escape responses, to alarm pheromone. These results suggest that divergent pheromone-mediated behaviours could alter predator–prey interactions in future environments.