The Physics of Radiation

This chapter discusses radiation, radiative transfer and the greenhouse effect. It starts by analysing radiation from a blackbody, identifying the key difference between shortwave radiation from the Sun and longwave radiation from Earth. It then describes the Planck function, which calculates the intensity of radiation emitted by a blackbody; the Stefan–Boltzmann law, which shows how changing the temperature of a blackbody affects the rate at which it emits radiation; Wien’s law, which calculates the wavelength of maximum emission; and Kirchhoff’s law of emission and absorption. These are then used to show the effect of increasing longwave-absorbing gases in the troposphere on the lower tropospheric temperature: the greenhouse gas effect. The chapter then describes the aspects of scattering, emission and absorption that are needed to understand the interaction of radiation with greenhouse gases. The chapter concludes by discussing radiative forcing and showing the current estimate of Earth’s energy balance.