Simple Climate Model

For today's climate the planetary emission temperature is approximately 255K, while the average surface temperature is approximately 288K! The difference is a result of the our atmosphere. The warming that results from the atmosphere is referred to as the Greenhouse effect.

In a cloud free atmosphere, shortwave radiation passes through the atmosphere and warms the surface. Longwave radiation emitted by the surface is partially absorbed by the Earth's atmosphere. The atmosphere also emits longwave radiation, but usually less radiation than the surface because the atmosphere is cooler. Gases that are transparent to solar radiation but emit and absorb longwave radiation are referred to as greenhouse gases. They include water vapor, carbon dioxide, and methane. Since, on average, the total solar radiation absorbed by Earth is balanced by the amount emitted to space, the atmosphere and surface are warmer than they would be without the greenhouse gases. To predict climate change, we must be capable of modeling climate.

This simple climate model demonstrates the effect of the atmosphere on surface temperature. For simplicity, the atmosphere is represented as a uniform shell surrounding the planet. In this model, the atmosphere does not absorb solar radiation; however, the atmosphere does absorb and emit infrared radiation. As with the first model, we assume energy balance: the absorbed radiation from the sun must balance the outgoing infrared radiation. In this model, an energy balance must exist at the top-of-atmosphere and at the surface.