What are greenhouse gases?
Atmospheric trace gases that keep the Earths surface warm are known as greenhouse gases. About three-quarters of the natural greenhouse effect is due to water vapour. The next most significant greenhouse gas is carbon dioxide. Methane, nitrous oxide, ozone in the lower atmosphere, and CFCs are also greenhouse gases.
Many chemical compounds found in the Earth’s atmosphere act as “greenhouse gases.” These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth’s surface, some of it is re-radiated back towards space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere. Many gases exhibit these “greenhouse” properties. Some of them occur in nature (water vapor, carbon dioxide, methane, and nitrous oxide), while others are exclusively human made (certain industrial gases). Over time, if atmospheric concentrations of greenhouse gases remain relatively stable, the amount of energy sent from the sun to the Earth’s surface should be about the same as the amount of energy radiated back into space, leaving the temperature of the Earth’s surface roughly constant. Why Are Atmospheric Levels Increasing?
Many chemical compounds present in Earth’s atmosphere behave as ‘greenhouse gases’. These are gases which allow direct sunlight (relative shortwave energy) to reach the Earth’s surface unimpeded. As the shortwave energy (that in the visible and ultraviolet portion of the spectra) heats the surface, longer-wave (infrared) energy (heat) is reradiated to the atmosphere. Greenhouse gases absorb this energy, thereby allowing less heat to escape back to space, and ‘trapping’ it in the lower atmosphere. Many greenhouse gases occur naturally in the atmosphere, such as carbon dioxide, methane, water vapor, and nitrous oxide, while others are synthetic. Those that are man-made include the chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) and Perfluorocarbons (PFCs), as well as sulfur hexafluoride (SF6). Atmospheric concentrations of both the natural and man-made gases have been rising over the last few centuries due to the industrial revolution.
Greenhouse gases are atmospheric gases that trap infrared radiation emitted from the earth, lower atmosphere, or clouds or aerosols and, as a result, cause positive radiative forcing (which means they enhance global warming). Many of these gases are naturally occurring and are essential to life on earth by providing a blanket for marine and terrestrial organisms. Without them, temperatures on earth would be intolerably cold. However, when their concentrations become too high, they may contribute to global warming to such an extent that they would make the earth intolerably hot. Nature has maintained these gases in the ‘tolerable’ range for billions of years, but human activities have been changing the concentrations of these gases since the start of the industrial revolution, around 1850.
The main greenhouse gases are water vapour, carbon dioxide, methane and nitrous oxide. They are called greenhouse gases because their role in the atmosphere is like the glass of a greenhouse (or a blanket), trapping heat. Without this protection the earth would be too cold for life. The concentration of greenhouse gases in the atmosphere is changing because of human activities.
