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 The input of energy from the sun and the release of energy (in the form of infrared radiation) by the Earth dominate the temperature dynamics of the planet. At the simplest level, then, understanding how the temperature of the Earth changes over time is just a matter of balancing an energy budget: if the Earth absorbs more energy than it emits, it will warm until it reaches thermal equilibrium. The simplest energy balance models, so-called “zero-dimensional energy balance models,” (ZDEBM) model the Earth and the Sun as point-like objects with particular temperatures, absorption characteristics, and emission characteristics. We can quantify the amount of energy actually reaching any particular region of the Earth (e.g. a piece of land, a layer of the atmosphere, or just the Earth simpliciter for the most basic ZDEBM) in terms of Watts per square meter (Wm$-2$). The amount of energy reaching a particular point at a given time is called the radiative forcing active on that point. Assuming that the Earth is in equilibrium—that is, assuming that the radiated energy and the absorbed energy are in balance—the simplest possible ZDEBM would look like this:

Here, $$S$$ represents the amount of solar energy input to the system (i.e. absorbed by the Earth), and $$F$$ represents the amount of energy radiated by the Earth. How much solar energy does the

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