Some of the radiation from the sun is in the visible light spectrum, meaning that you can see it. Finally, some of the radiation emitted by the sun is infrared radiation, a type of longwave radiation. Other forms of longwave radiation that you might be more familiar with include heat lamps, fires, microwaves and radiowaves. When radiation from the sun enters the Earth's atmosphere, some is absorbed by the atmosphere, some is reflected by clouds and by the surface of the Earth straight back into space, and some is absorbed by the surface of the Earth.
If the Earth simply kept absorbing incoming radiation and without emitting any of its own, it would get hotter and hotter through time.
Fortunately, the surface of the Earth also emits radiation. No matter what the incoming radiation wavelength is, the Earth emits the radiation back as infrared radiation.
Everything that has temperature emits infrared radiation. This includes the Earth. Diversity in Chemistry Awards Find awards and scholarships advancing diversity in the chemical sciences. Funding to support the advancement of the chemical sciences through research projects. ACS-Hach Programs Learn about financial support for future and current high school chemistry teachers.
Not really. There are only a few things you need to know, some of which are probably already familiar, to understand the basic idea of the greenhouse effect and why it is so important for the Earth. You know that when you stand in sunlight, you feel warmer than when you are in shadow, so you can feel that the light radiant energy the sun gives off carries energy that can warm an object—you. Although you usually cannot see it, all objects give off radiant energy and you can sometimes feel this energy.
For example, if there is a pot of hot water on your stove, you can feel the radiant energy it gives off without touching it. The amount of infrared radiation energy a warmed object gives off depends on its temperature—the higher the temperature, the more energy is given off. As you know, you can easily distinguish between a warm object and a hot object by holding your hand near the objects and feeling the difference in heating effect on your skin. These ideas are basic to understanding the energy balance between the sun and the Earth.
Just as sunlight warms you, it warms the surface of the Earth as well. The Earth does not continue to get hotter and hotter as it absorbs energy from the sun, because it gives off energy to space as invisible infrared radiation. In order to come into energy balance, the amount of infrared radiation energy given off by the Earth has to be equal to the amount of energy absorbed from the sunlight.
This makes carbon dioxide a good absorber of wavelengths falling in the infrared radiation region of the spectrum. Carbon dioxide constantly moves into and out of the atmosphere through four major processes: photosynthesis, respiration, organic decomposition or decay, and combustion or the burning of organic material. You will learn more about carbon dioxide and the carbon cycle in Module 4.
Methane CH4 is 30 times stronger than carbon dioxide as an absorber of infrared radiation. Methane, however, is present in smaller concentrations than carbon dioxide, so its net contribution to the greenhouse effect is not as large. Methane is also relatively short-lived lasting approximately 8 years in the atmosphere. Methane is produced when bacteria decompose organic plant and animal matter in such places as wetlands e.
Scientists are concerned about the concentration of methane increasing in regions where the Arctic and alpine permafrost is thawing and releasing methane as it warms.
Halocarbons are composed of carbon, chlorine, fluorine, and hydrogen. They include chlorofluorocarbons CFCs , which are man-made gases commonly used in refrigerators and air conditioners. Concentrations of CFC gases in the atmosphere are the highest of any of the halocarbons, and they can absorb more infrared radiation than any other greenhouse gas. The impact of 1 molecule of a CFC gas is equivalent to 10, molecules of carbon dioxide.
Nitrous oxide N2O , a relatively long-lived gas, has increased in atmospheric concentration due mainly to agriculture. Bacteria convert a small amount of this nitrate and ammonia into the form of nitrous oxide. Internal combustion engines also produce nitrous oxide. Ozone O3 is also a relatively minor greenhouse gas because it is found in relatively low concentrations in the troposphere the lowest layer of the atmosphere. In the troposphere, it is produced by a combination of pollutants — mostly hydrocarbons and nitrogen oxide compounds.
In the s, John Tyndall, an Irish scientist who was fascinated by the growth and formation of glaciers, wanted to test his ideas explaining how Earth maintained a fairly constant temperature.
He began a series of experiments to measure the amount of radiant heat infrared radiation that certain gases could absorb and transmit. Tyndall found that water vapor and carbon dioxide were good absorbers and emitters of infrared radiation. The relative importance of a greenhouse gas depends on its abundance in Earth's atmosphere and how much the gas can absorb specific wavelengths of energy.
0コメント