Scientists say that the Earth's temperatures are largely determined by the balance between the amount of sun energy entering the atmosphere and the amount of energy lost from the Earth into space. One of the most important climate mechanisms affecting this balance is a natural greenhouse effect—a band of gases that trap the heat emanating from the planet's surface similar to the way a glass greenhouse warms the air inside its glass walls during a cold winter. These gases include water vapor, methane, nitrous oxide, chlorofluorocarbons, and tropospheric ozone, but the single most important greenhouse gas is carbon dioxide, which accounts for the largest part of the greenhouse effect.
These greenhouse gases allow visible sunlight energy to penetrate deep into the atmosphere, where much of it is absorbed by the oceans and land masses. When this stored energy is released back toward space as infrared radiation, or heat, the greenhouse gases then act as an insulating blanket, absorbing and holding the heat in the lower atmosphere and helping to maintain the warm temperatures needed for humans to survive. As climate expert Mayer Hillman explains, "Without this natural greenhouse effect, the planet would be over 35° cooler than it is now—too cold for us to inhabit."3
The amount of heat trapped in this greenhouse process, however, varies depending on a number of factors. Some sunlight never reaches the Earth's surface because it is reflected back into space by clouds and various types of particles and pollutants in the air. In addition, different regions on the planet's surface reflect and absorb solar radiation differently. The ice caps at each of the Earth's poles, for example, act as giant mirrors that reflect back most of the sunlight that hits them, while exposed desert soils, oceans, and forested areas tend to absorb more of the sun's energy, helping to heat the atmosphere. A third factor is the concentration of greenhouse gases in the atmosphere, with higher levels producing more warming. All these elements must be in balance to produce average global temperatures that are in the relatively narrow range necessary for humans, plants, and animals to survive on the planet's fragile surface, seas, and skies. As British scientist and environmentalist James Lovelock has re-
This diagram shows the "greenhouse effect." Sunlight enters the atmosphere and heats the Earth; the heat is then reflected back into the atmosphere, but greenhouse gases cause some of the heat to be trapped from the planet's surface.
sunlight enters atmosphere, heating the Earth greenhouse gases.
\ ionosphere /
\ ionosphere /
minded us, the portion of the Earth that supports life is only "a thin spherical shell of land and water between the incandescent interior of the Earth and the upper atmosphere surrounding it."4
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.