Chapter summary

The functioning of Earth as a system can be seen in the global cycling of energy, water, and carbon and in other biogeochemical cycles. This chapter introduces the fundamental scientific concepts of energy, water, and biogeochemical cycles that regulate climate and link the atmosphere, hydrosphere, cryosphere, biosphere, and pedosphere. Heat is a form of kinetic energy that is transferred between materials due to temperature differences. Heat is transferred in the atmosphere by radiation, conduction, and convection. These flows of heat determine the balance of energy gained, lost, or stored by materials. The hydrologic cycle describes the cycling of water among land, ocean, and air, principally in terms of precipitation, evaporation, and the runoff of freshwater from land into oceans. The hydrologic cycle regulates the amount of water vapor in the air, which is the most important greenhouse gas. The increased capacity of air to hold moisture as temperature increases is an important thermodynamic principle that affects climate. In addition, considerable amounts of energy are required to change water among its solid, liquid, and vapor states. These phase changes are an important source of energy to drive weather and climate. Atmospheric gases interact with radiant energy flowing through the atmosphere to determine the planetary energy budget. Principal among these are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These gases cycle among the atmosphere, ocean, and land, regulated in part by biological and geochemical processes on land and ocean.