The Earth's Energy Balance

This lecture discusses the basics of climate science in order to support the discussion of deep decarbonization and other actions related to greenhouse gas emissions. As Joseph Fourier realized, the Earth’s temperature is determined by a kind of balance or equilibrium between the incoming energy of solar radiation and the outgoing energy that the earth radiates back to space. The energy that comes to the Earth as sunlight in ultraviolet radiation is either absorbed or reflected by the surface of the earth and the atmosphere, and the fact that the Earth itself radiates infrared energy is part of the study of blackbody radiation. The greenhouse gases trap this radiation and function as the blanket to warm the planet. How much of the coming radiation reflects back to space depends on the albedo of the Earth, or the reflectivity of the Earth as a result of cloud and ice cover, which becomes part of a feedback effect. It is important to understand the radiation spectrum of the incoming radiation and the absorption of the different wavelengths along the electromagnetic spectrum. The Stefan-Boltmann equation is used to determine that hot object will have more irradiance at high frequency ends of the spectrum, while cooler bodies have more radiation at the long-wavelength part of the spectrum. Greenhouse gases must have 3 atoms so that they can absorb the infrared radiation. Professor Sachs show s a graph which indicates warming since the 1950s, which shows average increases, but lots of variability in the upward trend. This video is part of the module The Basics of Climate Change Science.

This video is licensed under the CC BY-NC-SA license.