The Earth's reflected shortwave spectrum: present and future

Projected changes in the Earth system will likely be manifested in changes in reflected solar spectra. 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 spectra for simulations of present-day and of the 21st century. This general approach has been utilized successfully to detect and attribute forcings and feebacks in infrared spectra. However, it is novel for visible and NIR wavelengths due to the difficulty in producing realistic reflectance spectra and the tremendous computational expense in doing so. 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, and we find that the combination of longwave and shortwave spectra provide a more complete picture of the climate system. These findings suggest that the proposed NASA CLARREO mission to measure solar and infrared spectra might help detect climate forcings and feedbacks earlier in this century than conventional satellite instruments.1-2010-->