Aerosol radiative forcing is a critical, though variable and uncertain component of the global climate. Yet climate models rely on sparse information of the aerosol optical properties. In situ measurements, though important in many respects, seldom provide measurements of the undisturbed aerosol in the entire atmospheric column. Here we use 8 years of worldwide distributed data from the AERONET network of ground-based radi-ometers to remotely sense the aerosol absorption and other optical properties in several key locations. Established procedures for maintaining and calibrating the global network of radiometers, cloud screening and inversion techniques enable us to consistently retrieve the optical properties of aerosol in locations with varying emission sources and conditions. The multi-year, multi-instrument observations show robust differentiation in both the magnitude and spectral dependence of the absorption - a property driving aerosol climate forcing, for desert dust, biomass burning, urban-industrial and marine aerosols. Moreover, we observe significant variability of the absorption for the same aerosol type appearing due to different meteorological and source characteristics as well as different emission characteristics. We expect this aerosol characterization to help in refining aerosol optical models and in reducing uncertainties in satellite observations of the global aerosol and in modeling aerosol impacts on climate.