COS 229-3 - Altered Land Surface Albedo Accounts Substantial High Cooling Benefit in the Changing World

Abstract: Radiative forcing (RF) caused by altered surface albedo (∆α) of terrestrial ecosystems (RFα) is a major warming/cooling species for global climate and may have been significantly underestimated, likely attributable to: (i) lack of spatially representative in situ measurements; (ii) biased measurements from orbiting satellites; and/or (iii) crude estimates with very coarse spatial resolutions in many Earth System Models where albedo is estimated by the optical properties defined by lookup tables. We hypothesize that RFα accounts for a significantly larger proportion of the total RF in most terrestrial ecosystems than previously thought; its portion, however, is dependent on climate variability and other external forcing and varies across terrestrial land areas and over time. Using a large number of in situ measurements from global flux network, we present the magnitude and changes at multiple temporal scales among major terrestrial ecosystems. Contrary to the typical assumption in remote sensing modeling that the albedo of an ecosystem does not change over a period of several days, albedo appears highly dynamic at hourly to multiple-year scale and vary substantially by type among ecosystems in the same geographic locations. The diurnal changes in albedo at 8 experimental ecosystems in SW Michigan show clear low values at solar noon, but high in early/late of the ay, especially on clear days and with differences of >0.25. This difference is equivalent to 0.5 Mg C/ha/year of warming/cooling effects on climate, or ∼35-78% to the annual biogeochemical benefits provided from other bioenergy crops. Over an entire year, there also exhibit large changes in albedo in terrestrial ecosystems in temperate zone, ranging from < 0.18 in the growing season to >0.55 in the winter. Importantly, the albedo differences among the ecosystems are more pronounced in the winter months than in the summer. Urgent investigations are needed to compile all available albedo data and develop sound algorithms for Earth System Models, coupled with accurate land cover and land use changes, to advance our knowledge for understanding and forecasting the magnitude, temporal dynamics, and spatial variation of albedo, associated radiative forcing for Earth’s climate, and consequent credits for landowners.