The future evolution of the Earth's reflected shortwave spectrum

Projected changes to the Earth system will almost certainly change its reflected solar spectrum. This talk focuses on results from an Observational System Simulation Experiment (OSSE) to calculate the signals of future climate forcings and feedbacks in the reflected spectra. The OSSE combines IPCC AR4 simulations from the NCAR CCSM climate model with the Modtran radiative transfer code to calculate simulated spectra over the 21st century. This approach has been utilized successfully using infrared spectra, but it is novel for visible and NIR wavelengths. We find that expected forcings from increases in anthropogenic sulfate and carbonaceous aerosols are substantial and detectable from solar reflectance measurements and are confined spatially to lower latitudes. Low-cloud feedbacks and snow and ice-albedo responses to projected warming are readily detectable in the simulated spectra. We find that shortwave reflectance spectra are more suitable than infrared spectra for discerning changes in low clouds from changes in other properties of the climate system due to anthropogenic forcing. These findings suggest that the proposed NASA CLARREO Decadal Survey mission to measure solar and infrared spectra might help detect climate forcings and feedbacks earlier in this century than conventional satellite instruments.