Due to the rapid anthropogenic changes in global climate and ecosystems, it is needed to understand how these perturbations will influence central biotic interactions. The possible consequences of global environmental degradation can be obtained by studying how past climatic shifts have influenced diversity in plants and in insect herbivores. Especially the dramatic changes in global climate during the Cenozoic provide multiple possibilities for the mechanisms by which climatic shifts may drive diversity dynamics in plants and insects. Recent studies combining paleoclimatic reconstructions suggest that variation in global climate determines the distribution, abundance and diversity of plant clades and, hence, indirectly influences the balance between speciation and extinction in herbivore groups. However, available evidence suggests that positive and negative responses of insect diversity are lagged in relation to host-plant availability. Hence, although habitat loss and climate change may lead to extinctions in many plant groups, effects on insect diversity may become evident only over much longer time spans. The predicted large-scale movements of whole ecosystems may nevertheless lead to inconvenient surprises, following the emergence of novel competitive and parasitic associations in transitional communities.