The four major greenhouse gases – H2O, CO2, CH4 and N2O - and several other atmospheric gases like ozone absorb ENERGY provided by the SUN RADIATION. In a complicated pattern of back radiation and energy transfer in the atmosphere the result is TEMPERATURE increase when one or more of the greenhouse gas concentrations increase.
The SUN RADIATION is, however, also actively involved in the PHOTO SYNTHESIS processes who harness much of the Sun Radiation ENERGY by the building of green plants. The greenhouse gases – and particularly H2O and CO2 – are together with their corresponding elements taking part in perpetual cycles together with the climate system and in exchanges with other outside accumulations and systems. The effects of the photo synthesis processes are clearly visible in the variations of the CO2 concentrations in the atmosphere each year with diminishing concentrations during the summer months.
The photo synthesis processes are enormously large and going on all over our planet and can be summarized in a general “chemical equation”:
H2O + CO2 + sun light = O2 + CH2O (carbohydrates)
which says that light is absorbed and implies that the sun radiation energy is stored in the new chemical structures.Thus water and carbon dioxide are joined by absorbing the energy of the sun radiation and are building a vast amount of various ENERGY RICH carbohydrate structures such as food products in agricultural or garden enterprises and trees used for various products of the forest industries.
The products themselves and waste or surplus material from the production processes are energy rich and can be used to recover their energy content. If no quick energy recovery is done the normal circular processes in nature will make them decay and the parts going back into the photo synthesis processes components – water, carbon dioxide and energy - in due time, but slowly.
As examples of the energy content of the carbohydrates formed in the photo synthesis process can be mentioned food products like:
and forest products like:
All of the greenhouse gases and their elements are part of cycles that go on as far as the sun radiation supplies them with the energy required for the photosynthesis process. It could, however, be disrupted and/or partly stopped and has so been done like when large geological upheavals have taken place to make the ongoing biological processes and its living products have been buried deep under hard cover matter for millions of years. This buried material we now take up as energy rich fossil fuels that cause the global warming problems when they are burned. Other deposits like brown coal near the Earth´s surface or peat bogs or even nowadays big city dumps can be regarded as surplus energy rich material that have to a large extent dropped out of the cycles for the time being. They are recoverable in terms of greenhouse gases and energy.
H2O and CH4 take part in the hydrogen cycle which to a substantial degree is involved in various “water cycles” like i.e.
a) H2O in the “short water cycle”: evaporation and emission (gas phase) – condensation (cloud formation) – precipitation – evaporation – condensation - …. The “short cycle” is of particular interest because it cleans the troposphere from the particles which affect the absorption of the radiation and thereby the global warming.
b) H2O in other cycles starts as liquid water – joins with CO2 - forms a carbohydrate in a photosynthesis process – burnt – emitted to the atmosphere (gas phase) – condenses -…
c) CH4 emitted i.e. by decomposition of wastes and in wetlands, by ruminant digestion etc. – attacked by the highly reactive hydroxyl radicals in the atmosphere and the hydrogen atoms to become parts of water molecules – entering a ”water cycle -….
CO2 and CH4 take part in the carbon cycle which is exchanged among the biosphere, pedosphere, geosphere, hydrosphere and atmosphere through various processes among which the photosynthesis and processes in the oceans are important. CH4 molecules in the atmosphere are attacked by the highly reactive hydroxyl radicals there and converted to CO2 and H2O and then can enter the carbon cycle and the “water cycles”.
N2O takes part in the nitrogen cycle via various processes of which fertilization in agriculture, burning of biomass, fixation of nitrogen by some plants and cattle metabolism are important.
H2O, CO2 and N2O take part in the oxygen cycle which is kept going by the photosynthesis processes in plants and by plankton in the oceans.
H2O is different from the other greenhouse gases in several respects. During its cycles it passes through changes of states of aggregation (phases): the solid phase (ice, snow), the liquid phase (water) and the gaseous phase (vapor) while the other major greenhouse gases generally are in the gaseous state because their melting and vaporization temperatures are low. The tables in Figure 6 give some characteristic data for the four major greenhouse gases. Both the heat of vaporization and its specific heat are substantially higher for H2O than for the other greenhouse gases. The figures in the tables clearly demonstrate how superior water vapor is compared to the other three major greenhouse gases not only because it has an overwhelming much larger concentration in the atmosphere but also when it comes to storing and transporting matter and energy around the globe. Water vapor is also about 70 times more abundant in the atmosphere than CO2 and water as ice has a high heat of melting (abt. 334 kJ/ kilogram).
The water in the oceans is about 96.5% of all Earth water – a big reservoir. The nitrogen and oxygen gases in the atmosphere with abt. 78% and 21% respectively of all of its content of gases do not absorb any appreciable amounts of the solar radiation (except the greenhouse gases) and therefore do not play any more important role in the global warming drama than being big reservoirs.