The so-called greenhouse effect is an atmospheric process by which a portion of the sun's heat is trapped within the earth's atmosphere, making the earth's surface warmer than it would otherwise be. Life on earth is possible because there is liquid water, a blanket of life-supporting gases, and a climate neither too warm nor too cold. Human beings may now be altering this balance by adding unusual amounts of carbon dioxide to the atmosphere. This could make the global climate warmer than at any other time in human history. And this change would be irreversible.
The atmosphere contains 75% nitrogen, 23% oxygen, with argon, water vapor, and trace gases--including carbon dioxide--making up the remaining 2%. Carbon dioxide is an odorless, colorless gas which constitutes about 0.035% by volume of the atmosphere but whose significance far exceeds its relative scarcity. It is essential for photosynthesis, the process by which the sun's energy is converted into forms usable by plants and animals. It also helps regulate the critical heat balance of the planet, thus maintaining liquid water.
Carbon dioxide affects the heat balance by acting as a one-way screen. It is transparent to incoming visible sunlight and allows the sun's heat to warm the ocean and the land. But carbon-dioxide molecules block some of the infrared heat radiated back into space. This reflected heat is absorbed into the lower atmosphere. This is the so-called greenhouse effect . . .
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