Anthropogenic impact on the albedo of the earth

The impact of man and animal on the Earth's surface albedo (reflectivity), until recently believed to be quite small, or not considered at all, is analyzed. Discussion is presented of changes in the albedo due to the heat island effects of cities on snow cover, to agricultural cultivation, irrigation, and to overgrazing; the latter of which is emphasized. In arid climates, protected steppe areas have a low albedo due to dark plant debris accumulating on the crusted soil surface, whereas the same type of terrain, when overgrazed, exhibits a high albedo of trampled, crumbled soil. Extrapolating from observed spatial differences between overgrazed terrain and natural steppe, it is suggested that anthropogenic pressures mainly due to overgrazing could have had a very significant effect on the Earth's surface albedo both regionally and as a global average during the last few thousand years. The Earth's surface albedo presently might be 0.154 whereas it might have been 0.141 about 6000 years B.P. Thus, the surface albedo could have increased by Δa = 0.013, or by nearly 10% of its value when steppe areas were in their ‘virgin’ state. The hypothesized increase would be much larger in the Northern hemisphere than in the Southern. There are uncertainties even in the second digit of the suggested value for the present day albedo, and thus certainly for the albedo in the past. Seasonal mapping of the surface albedo from LANDSAT type satellites is recommended.