Much global change research is dedicated to discerning and documenting the impact of human activities on natural systems. Human population numbers were an estimated 750 million in the mid-1700s, rose to six billion in 1999 and could hit twelve billion before 2100 if current pace in growth continues. Human activities, which are known to be cumulatively altering the global environment, are responsible for greenhouse gas emissions from fossil fuel consumption, biomass burning, air and water pollution, and land cover/land use change. Far from being evenly distributed across the land surface, to a great extent human activities with environmental consequences are concentrated in or near human population centres. Having a capability for frequent global observation of a widespread and distinctly human activity that varies in intensity could substantially improve understanding of the scale of human enterprise and modelling its impact on the environment.