Global environmental changes require a comprehensive understanding of the Earth’s major systems, the important ways in which these are linked, as well as the impact of human activities on these systems. The major systems are the geosphere (processes of the Earth’s surface and interior), biosphere (life on land and in the sea), atmosphere (weather and climate), hydrosphere (water in the oceans, air, and on the continents), and cryosphere (snow- and ice-covered regions). The goal of Earth systems science is to obtain a scientific understanding of the entire system on a global scale. Recent studies of the continents, oceans, atmosphere, biosphere, and ice cover have revealed a far more complex and dynamic world than hitherto imagined.