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The Earth's Temperature: Certainly, the common temperature of the Earth has varied greatly throughout the last million years, from about 2°C (36°F) through the ice ages to about 15°C (59°F) through the warmer interglacial periods. We're now in an interglacial periodic and the Earth's average temperature for the last century averages 13.9°C (57°F). A lot of the study on the Earth's temperature has been an effort to know the coming and going of the ice ages. We now understand that the Earth's temperature is correlated with the Milankovitch cycles, which affect how much sunlight the Earth receives, but that's not the complete story. That greenhouse gases play a role in warming the Earth was shown by Joseph Fourier in the 1820s. Using the differential equations he developed for heat transfer, Fourier calculated that the Earth, considering its size and its distance from the Sun, ought to be considerably colder than it actually is. He proposed the Earth must certanly be kept warmer by its atmosphere, which acts much whilst the glass in a greenhouse. The specific amount of warming that may be attributed to the greenhouse effect was later found from the Stephen Boltzmann law, developed in early 1900s. If the Earth had no atmosphere, its average temperature could be 33°C lower, at -19.0°C (-2.2°F). Without greenhouse gases, the Earth will be a frozen block of ice. edg lit led

Greenhouse Gases: Heat energy leaves the Earth as infrared radiation, which makes up a the main spectrum that's absorbed by many molecules as they vibrate. As infrared radiation leaves the Earth, it's absorbed then reemitted in all directions, a few of it heading back toward the Earth where it further warms the Earth. In the 1850's, John Tyndall's infrared research found that nitrogen and oxygen, the major the different parts of the atmosphere, don't absorb infrared radiation. He learned that the molecules accountable for the greenhouse effect were water vapor and carbon dioxide. Water varies from a trace as much as about 4% with respect to the humidity; carbon dioxide's concentration was about 0.0028% in Tyndall's time. In spite of their low concentration, CO2 and H2O both absorb strongly in the infrared region of the spectrum. Also, radiation leaving the Earth must traverse several kilometers of atmosphere, greatly increasing the possibility of the radiation being absorbed and readmitted. Co2 plays a large role for its concentration, since it absorbs strongly in parts of the infrared spectrum where water does not.

Recent research by Kiehl and Tenebreth on the Earth's energy budget identified five naturally occurring gases that contribute to the greenhouse effect. The gases, with their contribution in both clear sky and cloudy conditions, are listed in the table. edg lit leds

All the greenhouse gases has several absorption bands, and there are a few parts of the spectrum where in actuality the bands overlap, as noted in the table. Once clouds form, the liquid droplets absorbed broadly across all the infrared region, so cloud formation reduces the contributions of the other gases. Overall, clouds and H2O account fully for about 75% of the greenhouse effect and carbon dioxide and the other greenhouse gases for approximately 25%. Some of the coldest nights on Earth are once the humidity is low and the night time is still and clear, whilst the contribution of H20 is reduced far below the 60% given in the table. Click here

The common residence time of a water molecule in the atmosphere is no more than nine days. Because precipitation removes water from the air such a short time, the concentration of water in the air varies from a trace in cold arid region as much as about 4% in warm humid regions. The common residence amount of time in the atmosphere of CH4 is 12 years, whilst the residence times of NO2 and CO2 are more than a century. Gases with long half-lives reside in the atmosphere long enough to become evenly distributed through the entire atmosphere. Ozone (O3), that includes a residence time of a couple of months, is constantly being formed in the atmosphere from photochemical processes, many which are initiated by methane and hydrocarbons.