Aerobiology at the global scale

A conceptual airscape model for biota flow in the atmosphere, in which the important factors influencing movement were scale-dependent, has been proposed by Isard & Gage (2001). For practical reasons, the global (or earth) scale has generally been neglected by aerobiologists. However, many of the most meaningful and relevant atmospheric biological invasions have taken place at this scale, notably movement between the Asian and African continents, or between Africa and South–America. Global scale motion systems are highly dependent on global wind belt and therefore are scaled to the year/continent temporal & spatial scales. It is probably the scale at which global climatic changes will have the most impact, as it is influenced by the phenological progression of seasons; and because it is the one governing the distribution of the largest patterns of airflow. At this scale, any changes can mean the appearance or closure of corridors between climate zones. These will involves the Hadley cells, the inter-tropical convergence zone, Rossby waves and middle tropospheric jet steams. After an assessment of these mechanisms and of the maximizing /minimizing view debate, using exogenous pollen examples; past case studies, mostly related to rust spores (of wheat, maize, and coffee) dispersion will be reviewed, and prospective new invasions will be considered specially in the context of global warming.