In a microbrew induced haze I attempted this question a couple of nights ago but came across as coherent as a monkey, so…
My understanding of albedo is as a general unitless measurement for the reflectivity of a surface. With that in mind and with the following picture Dawei posted of my home town (ironic) at first glace it certainly appears that farms would have a higher albedo than forested land and thus the increase of farmland would lead to a negative forcing shown in the second link.
However the darker color of the leaves absorbing more light and radiating heat can’t be compared to, say, dark rock because leaves convert the solar energy into chemical energy instead of simply storing and radiating heat. In fact a scant percentage of light absorbed by leaves is radiated as heat.
A cursory review of the literature shows no indication of this being taken into account in albedo measurements so is the negative forcing of land use changes truly accurate? Does the absorption of light and radiation of heat energy by land in fact play less of a negative role and potentially more of a positive one when the heat island effect of concrete, asphalt and steel is taken into account? What are your thoughts?
@Dana, maybe I’m misunderstanding your response, but my impression is that the land use albedo is more concerned with dark green forests converted to lighter colored farms causing more reflection and thus a negative forcing instead of absorbing radiation in excess of normal levels
@Dawei – I’m not comparing it to a rock, my point is that plant leaves (often darker colored) absorb light and convert it to chemical energy whereas a rock absorbs the light and immediately radiates heat to the surrounding environment which increases warming. Although virtual guys description of conversion of biomass to energy contradicts the idea. And I’m technically from Gainesville, just NW of city limits by a few miles.
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