What is the Greenhouse Effect?

The greenhouse effect refers to the fact that earth is surrounded by an atmosphere which acts like the transparent cover of a greenhouse, allowing sunlight to filter through while trapping heat.

Greenhouse gases are trace gases of mainly water vapor, carbon dioxide, methane, ozone, and nitrous oxide. The earth's atmosphere largely consists of nitrogen and oxygen, but they are not greenhouse gases nor do they contribute to the greenhouse effect.

During the daytime, the earth absorbs heat directly from the sun and reflects it out to space. Without an atmosphere causing a greenhouse effect, this heat would escape at night, in the absense of direct sunlight, and the earth's temperature would fall rapidly. Instead, gaseous molecules absorb the heat given off by the planet, and re-radiate it out in all directions, reabsorbing it and redistributing it again and again. This keeps the earth's surface relatively warm and the average temperature comfortable. The greenhouse effect is key in earth's ability to maintain a temperarture that sustains life.

A look to our neighboring planets of Venus and Mars shows what happens when the greenhouse effect - which is akin to a blanket covering the planet - becomes too thick or too thin. Temperatures on Venus soar because of its very thick blanket or atmosphere. The runaway greenhouse effect here is staggering. Mars on the other hand has such a thin blanket (atmosphere) and a weak greenhouse effect, that the planet is very cold. Nearly all of the heat that reaches Mars escapes. Relative distance from the Sun plays a part in the global temperatures of the inner planets, but a greenhouse effect, or lack thereof, is largely responsible for the climates on all these planets.

Scientists started using the term "greenhouse effect" in the 1800's. At that time it had no negative connotation. In the mid 1950's the term "greenhouse effect" began to be associated with global warming and also with the negative effects of our industrial age. This enhanced greenhouse effect, as it's sometimes referred to, is the result of burning fossil fuels. This releases additional carbon dioxide into the atmosphere at the rate of about 3 gigatons (3 billion metric tons) per year. Since carbon dioxide (CO2) absorbs heat, we can expect that significant increases in CO2 will tend to raise the global temperature, possibly contributing to global warming. Simply put, if greenhouse gases act like a blanket to keep our planet warm, we are thickening that blanket.

The natural greenhouse effect on Earth is responsible for life as we know it. We may, however, need to become better stewards of our greenhouse gases in order to preserve life.