The nitrogen and oxygen gases that make up most of the atmosphere do not absorb or emit thermal radiation. It is water vapor, carbon dioxide, and some other minor gases, present in much smaller amounts in the atmosphere that absorb some of the thermal radiation leaving the surface, acting as a partial blanket for that radiation, and causing the difference of about 21 ◦C between the actual mean surface temperature of the earth, which is around 15 ◦C, and the value of −6 ◦C that applies when the atmosphere contains only nitrogen.
This phenomenon is called the natural greenhouse effect, and gases are known as greenhouse gases. The basic science of the greenhouse effect has been known since the early 19th century when the similarity between the radiative properties of the Earth’s atmosphere and the glass in a greenhouse was first noted, hence the name “greenhouse effect”. “. Glasshouse”.
In a greenhouse, visible solar radiation passes almost, unhindered through the glass and is absorbed by the plants and soil inside. However, the thermal radiation emitted by the plants and the soil is absorbed by the glass, which emits part of it back into the greenhouse. The glass acts as a “radiant blanket” that helps keep the greenhouse warm. However, radiative transfer is just one of the ways heat moves in a greenhouse. By convection, in which warmer, less dense air flows upwards and cooler, denser air flows downwards.
A well-known example of this process is the domestic use of electric convection heaters, which heat a room by stimulating convection in it. The situation in the greenhouse is, therefore, more complicated than it would be if radiation were the only heating process. Mixing and convection are also present in the atmosphere, albeit on a much larger scale, and a proper understanding of the greenhouse effect requires both convective heat transfer processes in the atmosphere and radiation to be considered.
In fact, in the atmosphere itself (at least in the lower three-quarters of the atmosphere up to about 10 km altitude, which is called the troposphere), convection is the dominant process for transferring heat. Proceed as follows. The earth’s surface is heated by the absorbed sunlight. Air near the surface heats up and rises due to its lower density. As air rises, it expands and cools, just as air cools as it exits a tire valve. As some air masses rise, others sink, so the air rotates continuously while the various movements balance each other out: a situation of convective equilibrium. The temperature in the troposphere decreases with altitude at a rate determined by these convective processes; The drop with altitude averages about 6 ◦C per kilometer of altitude.
At some wavelengths in the infrared, in the absence of clouds, the atmosphere is largely transparent, just as it is in the visible part of the spectrum. If our eyes were sensitive to these wavelengths, we could see through the atmosphere to the sun, stars, and moon above, just as we can in the visible spectrum. At these wavelengths, all radiation emanating from the earth’s surface leaves the atmosphere. At other wavelengths, surface radiation is strongly absorbed by some gases present in the atmosphere, notably water vapor and carbon dioxide.
Absorbing gases in the atmosphere absorb part of the radiation emitted by the earth’s surface and in turn emit radiation into space. The amount of thermal radiation they emit depends on their temperature. These gases emit radiation into space from levels near the top of the atmosphere, typically between 5 and 10 km high. Here the temperature is much cooler (30 to 50 ◦C or more) than at the surface due to the convection processes mentioned above.
Because the gases are cold, they emit less radiation. These gases must therefore absorb some of the radiation emitted by the earth’s surface, but then emit much less radiation back into space. They, therefore, act as a radiant blanket over the surface. There must be a balance between incoming radiation and outgoing radiation from the upper atmosphere.
Clouds reflect part of the incoming solar radiation back into space. However, they also absorb and emit thermal radiation and have a similar masking effect as greenhouse gases. These two effects work in opposite directions: one (reflection of solar radiation) tends to cool the earth’s surface and the other (absorption of thermal radiation) tends to warm it. A careful examination of these two effects shows that the net effect of clouds on the total radiative balance leads on average to a slight cooling of the earth’s surface per square meter.
The temperature of the surface and thus of the upper atmosphere is adjusted in such a way that this equilibrium is maintained. Interestingly, the greenhouse effect can only work when there are cooler temperatures in the higher atmosphere. Therefore, without the structure of decreasing temperature with altitude, there would be no greenhouse effect on Earth.
The greenhouse effect is the increase in temperature of the earth due to certain gases in the atmosphere (e.g. water vapour, carbon dioxide, nitrous oxide, ozone, methane) trapping energy that originates from the sun. These gases are commonly referred to as greenhouse gases because they behave in a similar way to the glass panes in a greenhouse. Greenhouse glass lets light in but keeps heat from escaping, just like these gases work on Earth.
Sunlight enters the Earth’s atmosphere and passes through greenhouse gases. and the biosphere absorbs energy from sunlight. Once absorbed, this energy is released back into the atmosphere. Some of the energy returns to space, but much of it remains trapped in the atmosphere by greenhouse gases. This is a completely natural process and without these gases, all the heat would escape into space and the average temperature on Earth would be about 30 degrees Celsius (54 degrees Fahrenheit) cooler.
The greenhouse effect is a very important process because without the greenhouse effect the earth would not be hot enough for humans to live. But if the greenhouse effect gets stronger, it could make the Earth warmer than normal. Even a little extra heating can cause problems for people, plants and animals.
Some human activities also produce gases, and these gases continue to rise into the atmosphere. The change in the greenhouse gas balance has a significant impact on the entire planet. The burning of fossil fuels, coal, oil and natural gas releases carbon dioxide into the atmosphere. The burning of trees also produces a large amount of carbon dioxide. CFCs have been used in aerosols such as hairspray cans, refrigerators, and in the manufacture of plastic foams. As there are more greenhouse gases in the atmosphere, more heat is trapped, causing the Earth to warm.
This is known as global warming. Many scientists agree that human activity amplifies the natural greenhouse effect. If we continue to pollute the atmosphere with greenhouse gases, it will negatively affect the earth. The Earth’s temperature is increasing at an unprecedented rate.
To understand how rapidly global warming is accelerating, consider that throughout the 20th century, the average global temperature increased by about 0.6 degrees Celsius (just over 1 degree Fahrenheit) has increased. Using computer climate models, scientists estimate that the average global temperature will rise 1.4 degrees to 5.8 degrees Celsius (about 2.5 degrees to 10.5 degrees Fahrenheit) by 2100.