Comparing Laser-Based Measurements of Atmospheric Aerosols with Model Predictions—Impacts on Climate Prediction
Aerosols primarily scatter and absorb radiation back to space, shielding Earth’s surface from the sun’s energy and counteracting some of the warming induced by greenhouse gases. Global models have had some success in simulating the amount of aerosols in the lower atmosphere, but predictions have differed greatly among models and have undergone little constraint due to lack of measurements. Understanding the vertical distribution is important for predicting aerosol-cloud interactions and for accurate accounting of aerosol absorption enhancement over clouds. A team of international aerosol modelers, including Department of Energy scientists at Pacific Northwest National Laboratory, simulated global vertical distributions of aerosols and evaluated the results using measurements of aerosol extinction (scattering + absorption of sunlight) by a lidar instrument on a NASA satellite. All models simulated the observed decrease of the extinction with altitude; however, most models overestimated the extinction at altitudes between 6 and 10 km, particularly over the oceans and industrial regions. By predicting too much of the aerosol above clouds, the simulated aerosol is less easily scavenged and is more effective at making Earth appear darker from space and hence warming the Earth. This has implications for estimates of aerosol effects on climate and reveals a need for focused model development and testing.
Koffi, B., M. Schulz, F.-M. Bréon, J. Griesfeller, Y. Balkanski, S. Bauer, T. Berntsen, M. Chin, W. D. Collins, F. Dentener , T. Diehl, R. Easter, S. Ghan, P. Ginoux, S. Gong, L. W. Horowitz, T. Iversen, A. Kirkevåg, D. Koch, M. Krol, G. Myhre, P. Stier, T. Takemura, and D. Winker. 2012. “Application of the CALIOP Layer Product To Evaluate the Vertical Distribution of Aerosols Estimated by Global Models: AeroCom Phase I Results,” Journal of Geophysical Research 117, D10201. DOI: 10.1029/2011JD016858.