The knowledge of the role of aerosols in the climate system is acquiring a rich diversity. As examples, we consider two cases, one from the Earth’s recent past, and the other from the period of the Last Glacial Maximum (LGM). Aerosols arising as a result of human-induced emissions and originating in the continental areas of the Northern Hemisphere have significantly perturbed the radiative energy balance at the top-of-the-atmosphere and surface, and thus become a key ‘driver’ of the 20th century climate change. From model simulations and observations, the role of aerosols becomes discernible from the global to the continental scales. While they differ in their net climate effects with regards to the long-lived greenhouse gases, there exist important differences among the various types of aerosols. In the second example, the interaction involving circulation and dust emitted from the surface during the LGM has proven to be an intriguing challenge. Inferences from the Antarctic ice cores indicate a 10-100 times enhancement of dust relative to the present which has been difficult to explain. Using climate models, we identify the major factors likely responsible for the enhanced dust concentrations in the ice core during the LGM.