11/30/2016

Global warming

The average temperature of the Earth's climate system is increased during the last 100 years (see the image below). This rise of the temperature on earth was predicted because of the worldwide consumption of fossil fuels, like stone coal, petroleum and natural gas.


The combustion of these fossil resources results in an alteration of the worldwide ecological system, because it is a disturbance of the long term balance between the composing of carbon hydrate molecules – synthesized from carbon dioxide and water by plants – and the creation of carbon dioxide – from carbon and oxygen by the respiration of animals and other organism.

The result is a worldwide increase of carbon dioxide in the atmosphere. The image below shows a long term measurement of the carbon dioxide particles in the atmosphere at Hawaii. The small graph shows the annual cycle of the concentration, represented by the red line in the main graph.



The thermal radiation from the surface area of the planet – caused by the absorption of the radiation of electromagnetic waves, emitted by the sun – cannot pass the atmosphere of the earth without some absorption and radiation by the gasses in the air.
 

Our atmosphere is a mixture of different gasses: nitrogen, oxygen, argon and a couple of trace gases, like carbon dioxide, methane, hydrogen, etc. (see the image below).
 

Most of the gases in the atmosphere are elements, composed of one or 2 single type of atoms. However, carbon dioxide, water vapour and methane are compounds of different types of atoms. Carbon dioxide, methane and water vapour are known as greenhouse gasses, so there is a relation between the properties of these gases and their ability to “block” thermal radiation.


Single electromagnetic waves – photons – transport energy. The amount of transported energy is defined by the geometrical property of the wave: the wavelength. The speed of an electromagnetic wave is a constant – the speed of light – and every single wavelength  represents an amount of energy that’s a constant too, the constant of Planck (quantum mechanics). With other words: increasing the wavelength is decreasing the density of the transported energy. The geometrical properties of a material phenomenon – like an atom and a molecule – can only absorb energy of the right geometrical dimension.

Single atoms have – in relation to the radiated electromagnetic spectrum of the sun – only a couple of different geometrical dimensions: their electron configuration. Photon’s with the right wavelength are absorbed by an electron – mostly an electron in the outer shell – and after some time radiated again (emission spectrum).

Molecules like carbon dioxide, water vapour and methane have not only far more geometrical dimensions, the spatial volume of these molecules is very large in comparison to a single atom. Therefore, these molecules can absorb a large range of different electromagnetic wavelengths, including infrared radiation. 



The image above shows the atmospheric absorption within the electromagnetic spectrum by a couple of atmospheric gasses (oxygen, water vapour and carbon dioxide). The diagram shows the wide range of absorption by carbon dioxide and water vapour.

Atmospheric absorption of infrared radiation occurs not only for the radiation of absorbed heat by the surface area of the planet, the incoming infrared radiation of the sun is partly absorbed too. The image below shows the spectrum.

 

However, the irradiance of the spectrum of the solar radiation is not equal to the irradiance of the spectrum of the radiation by the surface of the earth because absorbed high frequencies are radiated at lower frequencies during the night time. That's why the increase of a greenhouse gas don't keep the balance of the incoming and emitted radiation at a stationary level.

So greenhouse gasses cannot "block" infra red radiation emitted by the surface area of the planet. These gases delay the radiation to outer space by absorbing different electromagnetic frequencies and by subsequently emitting the radiation in all directions. Therefore, the total effect of the raise of carbon dioxide in the atmosphere is a raise of thermal radiation.



Next chapter:  "Heat accumulation"