Title : Human-induced ground albedo increasing: How does it affect climate change
Abstract:
I n the last decades, human activities have generated increasing in ground albedo produced by deforestation and overbuilding. Man-made deforestation has caused desertification and a consequent increasing of ground reflected solar radiation. In addition, the areas of cemented land have increased more and more because a large increase in the demand for increasingly wealthy homes and workplaces, inducing overbuilding. Also this phenomenon has given rise to an increasing in ground reflected solar radiation. Both effects have induced an increasing of ground albedo coefficient. The ground albedo solar radiation corresponds to the ratio of reflected/ to the incident light at a considered surface and can be calculated by empirical models.
Overgrazing and deforestation influence Earth’s climate because albedo increasing induced by desertification causes an increasing of greenhouse effect in the troposphere.
Nevertheless, ground albedo variations can also affect the energy balance between Earth and air, influencing locally and globally the state of troposphere. In particular it was shown that ground albedo increasing induces surface latent and sensible heat flux decreasing at the surface because of the reduction of solar radiation energy absorbed at the surface, resulting in a reduction in convection and precipitation [1, 2]. Furthermore, another effect due to ground albedo increasing has to be taken into account, that is, the increasing latent and sensible heat flux in air layers in the proximity of the ground, according to the equation Ir = Hg ρ (1 – cos β )/2 in which Ir is the ground reflected solar radiation, Hg is the monthly average of daily global solar radiation impinging on a horizontal surface at a location, β is the slope of a generic air layer and ρ the ground albedo coefficient [3]. The annual global solar radiation absorbed by a hypothetical air surface is given by IT = Ib + Id + Ir where Ib is the direct solar radiation and Id the diffuse solar radiation [3]. It can be calculated using some empirical models and algorithms. The algorithm of [4, 5] and the ground albedo coefficients ρ = 0.10, ρ = 0.45 and ρ = 0.55 corresponding to the conifer forest [6], the desert sand [7] and an average value of cemented soil [8, 9], respectively, were used. Using recent results regarding the Sahara desert expansion [10] and the increase of cemented soil area in Earth’s surface due to overbuilding [11], it resulted that the annual global solar radiation acquired by troposphere layers neighboring desert or cemented soil, increases significantly (about 3.5 %) with respect to the annual global solar radiation collected by air layers in proximity of forested ground. This circumstance induces a rise of heat and temperature and a consequent decrease in density in air layers neighboring desert or cemented soil. As a result, air motions in vertical direction following convention rules in meteorology occur, causing air flows between these differently heated air areas due to thermal gradient, as schematized in Fig.1. This thermoconvective process related to humaninduced ground albedo increasing represents a cofactor that contributes to greenhouse effect and climatic change.
