Fig. 1. Researchers study terrestrial ecological processes by measuring land-to-air carbon dioxide fluxes using surface-based instruments, satellites, and laboratory studies. They use their understanding of the processes and empirical relationships derived from these types of studies to estimate carbon stocks and fluxes at regional to global scales. Photo credits: Clockwise from top left: NOAA, NASA, John Lenters, NASA, Juan Botella, Juan Botella, USDA-NRCS.