Assessing Human Impacts on Climate System over Global Urban Areas

Urbanization as a form of rapid change in global land cover will contribute to changes of the climate system. Although the climate impacts of urban growth has been studied since the 1950s, it has only been observed through changes of surface air temperature. The past use of remote sensing to look at small areas suggests that such an approach could be very useful on larger scales. However, what is best to observe in such a context and how it might be related to the simulations of global climate models should first be addressed. Recent observations from the MODerate Resolution Imaging Spectroradiometer (MODIS) on the NASA terra satellite can be applied to monitor urban land surface and atmospheric disturbances caused by human activities. Analyzing all of the global urban pixels for land surface skin temperature, albedo, emissivity, land cover, as well as clouds and aerosol properties, we observe that climae is modified over urban areas from the decrease of surface albedo and emissivity, and from the increase of clouds and sulfate aerosol optical depth. The unique strengths of MODIS data (global coverage, fine resolution, simultaneous measurements of various important surface and atmospheric variables) make it possible to investigate all the cities over the globe, and so advance the understanding of what is the range of urbanization effects, what determine these effects, and so suggest how impacts of urban physical processes may be addressed through use of global climate models.