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Simulation studies for the detection of changes in broadband albedo and...

Feldman, D., C. A. Algieri, W. D. Collins, Y. L. Roberts, and P. Pilewskie (2011), Simulation studies for the detection of changes in broadband albedo and shortwave nadir reflectance spectra under a climate change scenario, J. Geophys. Res., 116, D24103, doi:10.1029/2011JD016407.

Climate forcing by greenhouse gases and aerosols and climate feedbacks from snow, sea-ice, and clouds all significantly impact the future evolution of the climate system’s shortwave energy budget. We examine prospects for tracking changes in these forcings and feedbacks using top-of-atmosphere measurements of shortwave reflected radiation. We quantify the extent to which spectral measurements may reduce the time required to detect changes in the climate the climate system with high statistical confidence relative to conventional broadband measurements. We have developed an Observing System Simulation Experiment (OSSE) based on the Community Climate System Model 3.0 for the NASA CLARREO mission and have analyzed forced and unforced simulations of the 21st Century from the Intergovernmental Panel on Climate Change assessments. We find that changes in the simulated nadir spectral reflectance measurements in the visible window and between near-infrared water-vapor overtone channels under clear-sky conditions are detectible faster than the corresponding changes in broadband albedo, with many trends detectible within a five-year satellite mission lifetime. Under all-sky conditions, the superposition of unforced cloud variability on the secular climate trends lengthens the times required for climate-change detection in both the spectral and broadband data. However, migration of the ITCZ and stratus regions can be detected after 16–18 years of observation while broadband albedo measurements require 33–61 years of observation. We find that measurement uncertainty and instrument drift significantly lengthen detection times for broadband albedo and spectral reflectances in window channels but do not have the same effect for spectral measurements in water vapor bands.

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