Economic valuation of Earth's critical zone: Framework, theory and methods

The economic valuation of ecosystem services derived from Earth's critical zone has primarily concentrated on vegetation and surface waters or on a few selected aboveground services; however, the economic value of ecosystem services provided by the atmosphere and shallow lithosphere has not yet been considered substantially. In order to address this research gap, we propose a more explicit and rigorous definition of critical zone services as the human benefits provided by Earth's critical zone. This concept brings a more complete inventory of stocks and flows upon which critical zone valuation methods are based. By considering the 5 interconnected components (atmosphere, vegetation, soil, surface water, groundwater) of Earth's critical zone, we identify from literature review a wide range of critical zone services and classify them into three categories (provisioning, regulating and cultural) defined in the Common International Classification of Ecosystem Services. We do not consider supporting services, whose influence is intrinsic to the values of the other classes, specifically to avoid double accounting. Based on the defined critical zone services, we present a methodology enabling economic valuation of Earth's critical zone that is consistent with partial equilibrium theory and accounts for biophysical and economic input to the analysis. This approach achieves two significant aims that 1) incorporate recent new natural sciences concepts and knowledge in evaluating the structure and function of the critical zone into methods of applied economics and 2) provide natural environmental scientists with access to simplified theory and practice of applied economics that is relevant to valuation methods at the location-specific physical scale of the critical zone. The proposed methodology can be used as a quantitative management tool for economists and policy makers to more transparently enumerate the provision of services arising from the biophysical functioning of the whole of Earth's critical zone in the face of increased pressures of increased population, land use intensification, and climate change.