The Earth's Radiation Energy Balance
An object will warm or cool depending on its energy imbalances. If the object receives more energy than it losses, the object will warm. If the object losses more energy than it receives it will cool, and if the energy gains equal the energy losses, there is no temperature change. Methods of transferring energy in the atmosphere include conduction, convection, latent heating, advection and radiation. The method of transferring energy through radiative processes is different from the other mechanisms in that the transfer process does not require molecules. If we consider the planet as a whole, the Earth exchanges energy with its environment (the solar system) via radiation. The radiation balance of the planet is a fundamental parameter that determines our climate. This balance includes energy from the sun, or solar energy, which is an energy source for the planet. Any object that has a temperature emits radiation, we refer to this energy as terrestrial or infrared energy. The hotter the object, the greater the amount of energy emitted. Terrestrial energy can cool or warm an object depending on the object's temperature, and the temperature of the surrounding environment.
Imagine that you are at a barn fire on a cool autumn evening. As you face the fire, your front warms because you are receiving more energy from the fire than you are losing. Your back cools down and gets cold because you are losing more energy than you receive from the cooler air around you. You experience a local energy imbalance, your front warms and your back gets cold. If you get too uncomfortable, you can turn around, allowing your back to warm-up and your front to cool-down. As we look at the radiation balance of the planet, just because a given region may be receiving more radiative energy than it is losing does not mean the region's temperature is increasing. The atmosphere and ocean may move this excess energy to a different region of the globe, perhaps one that is losing more energy than it is receiving.
The determination of the Earth's radiation budget is essential to atmospheric modeling and climate studies. Radiation budget experiments have used satellites to measure the fundamental radiation parameters -- the amount of solar energy received by the planet, the planetary albedo (the portion of incoming solar radiation that is reflected back to space), the emitted terrestrial radiation (also referred to as the outgoing longwave radiation -- OLR), and the net planetary energy balance (the difference between the absorbed solar energy and the OLR). The most recent experiment to measure these parameters is the NASA Earth Radiation Budget Experiment or ERBE. Results from ERBE are presented below, you can find more information about ERBE in the papers cited below. As you look at these maps, the month is printed in the upper left hand corner and the legend is given along the bottom of the figure. Albedo values are given in units of percent reflectance, all others are in terms of energy per unit time per unit area (Watts per square meter).