It is the Goldilocks Principle. The temperature of earth is perfect for living as it is an average temperature between the freezing point of water and the boiling point of water which makes it most appropriate planet to dwell on. The comfortable temperature of earth cannot be explained by merely saying that earth is at the right distance from the sun. Neither it is very close like Venus nor far distant like Mars. The appropriateness of earth is also due to perfect atmosphere. The atmosphere of Venus is hellish. It is so hot that living or even staying on it is impossible. The atmosphere of Mars is freezing, shivering, and so cold to support life. The Martian type atmosphere on earth could destroy the moderation of earth that has made the life possible. The surface temperature of Venus is 450 degrees centigrade and of Mars is -53 degree centigrade, where the temperature of earth is 13 degree centigrade.
Why the temperature of earth is so moderate? How it is kept stable? What is the relationship between the earth’s climate and its distance from the sun? some of the parts of our earth’s atmosphere are of right thickness to serve as an insulating blanket that traps sufficient amount of energy to keep the temperature of this globe in the living range. The blanket is an aggregate of gases in the atmosphere, commonly known as green house gases. These gases trap the heat just like a glass of green house that is used to trap sunlight for keeping the environment warm. The Venus blanket is very thick where the Martian blanket is very thin. The green houses gases make the insulation effective. These gases are comprised of carbon dioxide (CO2), water vapors (H2O), methane (CH4) and nitrous oxide (N2O). Why and how these gases perform as an insulating blanket can be explained by highlighting a variety of some other relevant issues about the solar radiations and the structure of gases in the atmosphere.
Solar Radiation: Radiations of a wide range of spectrum are propagating from sun into the space. The quantity of these radiations is abundant. Most of this energy is in near visible or visible part of spectrum. The visible light has between 400 to 700 nano meters of narrow band which represents about 43 per cent of the total radiant energy coming out of the sun. The non-visible radiation account for about 7 to 8 per cent of the total radiation emitted by the sun but is of high quality as energy per photon is extensive. The energy increases with the decreasing wavelength. Ultraviolet light is energetic enough to break the stable biological molecules and generate skin cancer and sunburn. The remaining radiant energy is about 49 to 50 per cent and exist in wavelengths longer than the visible light, thus have lower energy. These rays lie in near infrared range that is between 700 to 1000 nano meters and the thermal infrared between 5 and 20 microns and the regions of far infrared. The atmosphere of earth is transparent to the visible light where it absorbs infrared and ultraviolet radiation before they penetrate the surface of the earth. About 51 per cent of radiation is absorbed by the earth, 20 per cent is reflected and scattered by the clouds, 19 per cent is absorbed by the clouds and the atmosphere, 6 per cent is scattered by the atmosphere whree 4 per cent is reflecetd back by the surface of earth.
The visible lifght is absorbed by the vegetation, ocean and land of the earth and transformed into heat or re-radiates as invisble infrared rays. If it is all about the earth’s atmosphere than the radition that are responsible for keeping the earth warm in day timnes must be emitted back by the surface during night, resulting in zero or even negative temperature on the earth. This does not happen as the molecules in the atmosphere of the earth not only aborb but also re-radiate the radiations in all possible directions. As a result the heat rediaated outsode earth, that is space, reduces. The green house gases enuire that the all heat may not return abck to the space so the activity on erath can be kept stable.
Greenhouse Gases: Carbon dioxide () is a greenhouse gas. It has 2 oxygen atoms and one carbon atom, each oxygen atom is bonded at each side of the carbon. The atoms can absorb infrared rays and start to vibrate, if the atoms are tightly bonded. At last the vibrating molecule will re-emit the radiation which will be possibly absorbed by another green house molecule. The process of continuous absorption-emission-absorption-emission-absorption results in keeping the temperature of earth warm near the surface and to preserve the planet from the coldness of the space.
Carbon dioxide (CO2), methane (), nitorus oxide (), water vapor (), and a few other gases are greenhouse gases. All these gases are composed of more than two atoms and are bound suitable to absorb and vibrate with the radiation. The N2 and O2 in the atmosphere are so tightly knit that they do not absorb the radiation but can only vibrate and likewise make the contribution in the green house effect.
Greenhouse Effect: The term green house was first used in 1800s. It was thought for, at that time, the atmosphere gases and not for any functions perform by these gases. In the mid of 1950s the green house effect emerged with a number of other climate related issues. Today the green house effect is only used as negative phenomena. The negative effects are only cast by the green house gases in case they are abundant. It is only because of the blessing of the green house gases that life on this planet is possible.
The temperature on earth is due to the action of atmosphere that is like green house, the temperature of earth is influenced by a number of factors that are also responsible for warming of cooling a green house.
The surface with which the sun light strikes first is of great significance in the atmospheric green house effect. The absorption, remittance and radiation of different parts of the earth is different. It is impossible that the forest, deserts, ocean, glacier, grasslands absorb, reflect and radiate the sun light likewise. When light encounters a white surface it is reflected straight back to the space, as a result the surface of ice is heated to the minimum level. On the contrary, when the radiation strikes some land of dark surface the amount of heat absorbed is maximum which results in heating up the temperature. Clouds perform an amazing part in controlling the green house effect as they reduce not only the amount of solar radiations that are coming to the planet but also depreciate the amount of rays that are emitted back to the space.
Albedo is the scientific term that is used to refer the amount of energy reflected back by a surface into the space. In order to predict the climate change at global level, it is crucial to understand the albedo effect at local, regional and global level.
There are certain trace gases that are transparent to the incoming visible light coming out of the sun where opaque to the radiation coming from the earth is a best example of digesting the science of atmosphere. It is just because of the blessing of green house effect that the earth is habitable. However, this is not the end. There is so much to enlighten. In our later posts we will try to bring into light what is green house effect and what factors affect it with the latest statistics on the heating up of the earth and many more.