Aerosol observations are available at scales from local aircraft measurements through regional sampling networks like IMPROVE and up to global satellite measurements. I will show examples of how IMPROVE and MISR data can be used to constrain trends in the direct radiative forcing by aerosols. For example, the US has already made substantial reductions in black carbon emissions but the net change in direct aerosol forcing was toward warming. Globally, there are strong regional trends in the last decade but they cancel to a larger degree than might be expected. Local measurements can show the large role played by hygroscopic growth and boundary layer depth in aerosol radiative forcing. In the Chemical Sciences Division, we are developing new instruments to measure properties of aerosols closely related to climate forcing and to augment AERONET observations.