9. The Origins of Climate Science: The Idea of Energy Balance

Heat is the kinetic motion of atoms or molecules. The Laws of Thermodynamics were developed in the middle of the nineteenth century. These laws state that energy cannot be created or destroyed, it can only change form; that two nearby systems, each internally in thermodynamic equilibrium, but not in equilibrium with each other, will exchange matter or energy and reach a mutual thermodynamic equilibrium; and, as the temperature approaches absolute zero, the entropy of a system approaches a minimum. Entropy is energy that is no longer available for doing mechanical work; it is the random motion of atoms or molecules; it is waste heat; it cannot be used to do anything: it is Mother Nature’s tax on everything. The ability of some gases to absorb and reradiate energy and to heat the air was discovered and measured in the middle of the nineteenth century. The idea of the climate being the result of a balance between the energy received and emitted by the Earth arose but lacked a formal analysis. The concept of a ‘black body,’ a perfect absorber and emitter of energy was developed in the latter half of that century. It formed the basis for understanding the energy balance of incoming radiation from the Sun and outgoing radiation from the Earth, and hence the planetary temperature.