Atmospheric change studies conducted in free air concentration enrichment (FACE) systems and open-topped chambers have increased understanding of how factors, such as rising CO2 and O3 levels, impact the development of plant disease epidemics. Using these systems, plant scientists have been able to study host/pathogen systems under real-world conditions where variations in multiple environmental parameters impact disease outcomes. Results from these studies are useful for evaluating earlier predictions on plant responses to climate-change parameters and the resulting impacts on plant disease epidemics. Some of these predictions have been verified, whilst others have yet to be tested. Significant interactions among climate-change parameters are highlighting the importance of conducting studies under real-world conditions. The development of molecular and gene expression tools is allowing the fine scale mechanisms responsible for the observed reactions to be determined, and should increase the ability to predict plant disease outcomes under future climatic conditions.