Earth does not consume energy. Neither do we nor does our energy system. Rather, we consume exergy. So using an exergy optic should be preferred when we plan future hydrogen-electricity systems. in this article, we provide a perspective on the exergy optic from the viewpoint of Earth's major energy-transaction constituencies. We first consider the Earth as a whole and then consider the following constituencies: the biosphere, people and civilization's energy system. Our objectives are to understand better the nature and sources of thermodynamic losses and to provide a background against which future hydrogen opportunities may be evaluated. As a codicil, we hope our results can improve our understanding of how people, civilizations and nature operate, and are connected. In a companion article, representative components within the energy system hierarchy (e.g., Niagara Falls, home heating systems and fuel cells) are considered. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.