Evenly blackbody radiation absorption and radiation in each band. General gas is not in bold, will selectively absorb certain bands of radiation. Many of the Earth atmospheric gases absorb hardly visible, but specialized to absorb long-wave radiation. Figure 3-3 are a variety of gases in the absorption rate band. For example, water vapor (H2O) in less than 0.8μ m band absorption rate is almost zero, but in the longer-wave part of (for example, 5μ m) the absorption rate of almost 1, which is completely absorbed. Carbon dioxide (CO2) in the wavelength greater than 15μ m above the radiation has excellent absorption rate. Oxygen (O2), ozone (O3), nitrous oxide (N2O), methane (CH4), also have similar characteristics. In addition to absorbing long-wave radiation, oxygen and ozone more absorbing a large portion of the ultraviolet light, so that life on Earth immune to UV radiation poisoning .
These are good at absorbing long-wave radiation but do not like to absorb short-wave radiation of the gas, allowing about 50% of solar radiation through the atmosphere, surface absorption, but almost all of the surface to intercept and atmospheric radiation of energy, reduce energy loss, and then the emitted, making the surface and tropospheric temperature. If the top of the atmosphere solar radiation intensity (342 Wm-2) as 100 units, 89 units of surface absorbed from the atmosphere to the surface radiation of the long-wave radiation, is much larger than its short-wave radiation absorbed by the volume (about 50 units). At night, atmospheric long-wave radiation to radiation, so that the surface is not due to lack of solar radiation has become too cold. The impact of these gases similar agricultural greenhouse warming effect, so called greenhouse gases, their impact is called the greenhouse effect. The existence of atmospheric warming is not only the surface, but also lowered the temperature difference between day and night.
If we consider the radiative properties of the atmosphere, but does not consider the characteristics of the atmosphere can flow, the vertical distribution of atmospheric temperature should be the dotted line in Figure 3-4, the actual temperature distribution, compared with solid line. Comparing the two, we found that only consider the radiation balance, surface temperature much higher than the actual temperature, and the tropopause (about 10 kilometers) is too low, and therefore the vertical temperature lapse rate is far greater than the actual vertical atmospheric lapse rate. This one atmospheric state is bound to a very unstable, prone to intense convection, so that hot air rising, cold air drop, the net effect for the heat to upload. Near surface air temperature drop, high temperature increased, so that the temperature of the vertical temperature trends Figure 3-4 in the solid line. This boil water in the stove on very similar process: teapot in the rolling water, will be provided by the fire's spread the heat evenly, until all the water to reach boiling point.
The greenhouse effect not only occurred in the Earth, Venus and Mars, the main ingredient for the carbon dioxide atmosphere. Atmospheric greenhouse effect of Venus up to 523 ℃, the Martian atmosphere is too thin, the greenhouse effect is only 10 ℃, while the Earth's atmosphere between the two for 33 ℃ (Table 3.1). Strictly speaking, the Earth's atmospheric greenhouse effect should be 82 ℃, because if we do not consider the vertical movement of atmospheric, land surface temperature from -15 ℃ up to 67 ℃ (Figure 3-4 the dotted line). We measured the surface temperature (15 ℃) are actually adjusted by the exercise of atmospheric temperature.
The greenhouse effect since ancient times. Was born in the earth 46 million years ago, when the intensity of the sun only about the current 70%. Solar intensity of 1% of the change, which is equivalent to the surface temperature of 1 ~ 2 ℃ changes. Therefore, if the Earth's climate is only affected by the impact of solar radiation in the radiation balance, the ancient Earth's atmosphere should be dozens of degrees lower than at present. At that time, the earth will not be a blue, full of water planet, but a white hockey. However, none of a variety of paleoclimate data show the Earth once in such a cold climate. This is the so-called contradictions of the sun weak (weak sun paradox). Scientists found that when the newly formed earth, volcanic activity, many emitting carbon dioxide, has become the main component of the atmosphere. Carbon dioxide greenhouse effect, so a lot of atmospheric temperature. Therefore, although solar radiation is weak, but the Earth's climate is not too cold. This one with Venus and Mars similar.
At present, the main component of atmospheric nitrogen (N2) and oxygen (O2) and a far cry from the early atmospheric composition. This is because the original biological emergence of algae, the photosynthesis, carbon dioxide release of oxygen, gradually transforming the composition of the atmosphere. Today, most of the carbon stored in the earth's crust and oceans, the atmosphere was full of oxygen. Venus and Mars, because no biological effects of early atmospheric composition is therefore retained. Scientists also found a number of times, paleoclimate Megathermal emergence are related to carbon dioxide (from volcanic eruptions) an increase. From the above discussion, we know that the greenhouse effect is a natural phenomenon, but since the opening day of pangu have. As long as there is the atmosphere, the greenhouse effect may have.
Changes in carbon dioxide levels can affect the climate, but to create the current atmospheric temperature distribution is a major factor in water vapor. Atmospheric water vapor amount of small, only 0.5 percent less than the total mass of the atmosphere, but water is apart from the sun, the impact of biotechnology and climate biggest material. Scientists simulate the vertical distribution of atmospheric temperature and found that as long as the mode Add the actual water vapor content of the observed, simulated atmospheric vertical temperature distribution with the actual situation on the order of magnitude . If we add carbon dioxide, the temperature further enhance 10K, but does not change the temperature distribution; stratosphere (10 km) temperature with a high increase in the required addition of ozone can add analog out. This simulation, because not taken into consideration the effects of clouds, tropospheric temperature higher than a lot of observations. The study pointed out that the biggest impact of greenhouse gases are water vapor, which contributed 80% of the greenhouse effect, not only determines the vertical distribution of atmospheric temperature, but also created a warm Earth's climate. Relatively speaking, the carbon dioxide is the climate becomes warmer.
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