Global and Local Effect of Increasing Land Surface Albedo as a Geo-Engineering Adaptation/Mitigation Option: A Study Case of Mediterranean Greenhouse Farming

Abstract

Current warming trends have been generated by a recent imbalance in the Earth’s energy budget, characterized by the reduction in 2.6 Wm-2 of the global mean annual outgoing terrestrial longwave (LW) radiation from pre-industrial times (Forster et al., 2007). As a result, there is an excess of incoming solar shortwave (SW) radiation that is driving surface and atmospheric temperatures to higher values of equilibrium. This alteration is called radiative forcing (RF) of the climate, and is very probably originated on the unprecedented growth of greenhouse gases (GHGs) in the atmosphere due to human activities. The reduction to zero emissions might be the only long term effective action to stabilize temperatures at reasonable levels (Mathews & Caldeira, 2008), before impacts are too catastrophic to manage. But on the other hand, in recent years there is a growing interest in the design of geo-engineering strategies to offset this warming exerted by GHGs through radiative rebalancing of the Earth s energy budget. These proposals can be divided in two groups, according to which parte of the energy budget is addressed for rebalancing. The first group, named as Solar Radiation Management tecniques (SRM), joins up all strategies that attempt to reduce the net amount of SW radiation absorbed by the Earth, by limiting the solar energy reaching the planet. SRM can be achieved by increasing the reflectivity or “albedo” of the Earth to SW radiation at different levels of the atmosphere, at the surface, or even from the outer space. The second group, called Carbon Dioxide Removal (CDR), groups all strategies that aim to increase the amount of LW radiation emitted by the Earth, directly counteracting the greenhouse effect by actively removing the excess CO2 from the atmosphere, and storing it in long term reservoirs. One practical way to make comparisons among the potential impacts on climate of different agents is using estimated RF values, thought it must be borne in mind that this metric does not fully represent their overall impact on climate (Pielke et al., 2002), and that further modelling studies are required. Lenton & Vaughan (2009) have recently quantified in terms of RF the climate cooling potential of a wide range of geo-engineering proposals discussed in the recent literature (Boyd, 2008), taking into account their current feasibility of implementation. In the case of proposals aimed to increase the Earth’s albedo at low levels, their estimation of RF potentials (SWRF) is summarized in the Table 1: