Another global environmental issue we face is the greenhouse effect. Agriculture and horticulture widely employ greenhouses made of glass or vinyl. These materials allow visible light and near-infrared rays in the wavelength range between 400 nm to 3,000 nm to easily pass through, while making it difficult for infrared rays between 10,000 nm and 20,000 nm to do so. Infrared rays play a central role in the radiation of heat, which is why the inside of a greenhouse heats up.

Water vapor such as clouds, carbon dioxide, methane, and Freon are some of the gases that have the same effect on the earth as glass and vinyl do on greenhouses. They are therefore called greenhouse gases.

The specific heats of these gases are larger than that of air, which comprises mostly oxygen and nitrogen, so it becomes difficult to lower the temperature of these gases once it begins to rise. Until today, the earth's temperature has been determined through a precise balance between the atmosphere and the plant and animal ecosystem.

However, the greenhouse effect is progressing owing to recent rapid increases in carbon dioxide, and concerns are that this will lead to a rise in atmospheric temperature around the world.