Is there overshoot of planetary limits? New indicators of human appropriation of the global biogeochemical cycles relative to their regenerative capacity based on 'ecotime' analysis

The global biogeochemical cycles are recognised as extremely important processes operating within the Earth's (geo)biosphere. However, there are currently few methods available through which we can understand and communicate humanity's dependence on these cycles. This paper presents a novel method, based on input-output analysis, for deriving a suite of indicators describing the level at which the global economy, through its transformation of useful resources (i.e. raw materials) into residuals (i.e. wastes, pollutants, emissions), is appropriating biogeochemical processes. Furthermore, significant insight into the scale of the global economic system is gained by comparing the rate of human appropriation of biogeochemical cycling with that of the biosphere's regenerative capacity. In order to calculate these indicators, we create a new concept of 'ecotime', defined as the average biogeochemical cycling time available for matter held within differing types of environmental commodities (e.g. carbon dioxide, plants, fossil fuels) to reach biogeochemical processes under consideration. Resources used by the global economy generally have long ecotimes, while the residuals produced by economic activities generally have short ecotimes. Applying our method to an extensive database encompassing the key biogeochemical cycles, it is found that humans are placing significant pressure on these cycles. (C) 2014 Elsevier B.V. All rights reserved.