Cycles of the major greenhouse gases and their elements.
All and each one of the four major greenhouse gases and their corresponding elements take part in perpetual cycles within the climate systems and in exchanges with other outside accumulations and systems.
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.
N2O takes part in the nitrogen cycle through various processes of which fertilization in agriculture, burning of biomass and cattle metabolism are important.
H2O, CO2 and N2O take part in the oxygen cycle which is kept going by the photosynthesis process in plants and by plankton of the oceans.
H2O and CH4 also take part in the hydrogen cycle which is also involved in the other three element cycles mentioned above and recycles as in various biogeochemical cycles.
Of special interest for the climate is the “short hydrogen cycle” (the “water cycle”) – water emission and evaporation→cloud formation and transport→precipitation→transport to reservoir → evaporation → cloud formation and transport →…….. An important effect of the “water cycle” is that the condensation and precipitation therein cleans the troposphere to a smaller or larger degree from the particles which to a substantial degree affects the absorption of the radiation and thereby affects the global warming.
H2O passes through changes of states of aggregation (phases): the solid phase (ice), the liquid phase (water) and the gaseous phase (water vapor) during its cycles. The other major greenhouse gases are generally always in the gaseous state because their melting temperatures and vaporization temperatures are low. The major greenhouse gases can also change by taking part in various processes during their cycles: chemical by the photosynthesis and by burning, biological by decay under the influence of bacteria etc. Industrial production processes, agriculture, silviculture and households can be involved. During and between the different states of aggregation, during chemical reactions and industrial processes or human activities of various kinds energy and matter can be used or produced, stored or released.
The continuing increases and additions to the cycles of the various greenhouse gases originating from the since long time ago deposited fossil fuels means that there is also a continuing build-up of higher contents of greenhouse gases and latent energy in the atmosphere (climate system) even if i.e. more CO2 will be taken up by the growing plants at the higher temperatures and more energy will be radiated out into space.
The following table gives some characteristic data for the four major greenhouse gases:
|Gas||Melting temperature °Centigrade||Boiling temperature °Centigrade||Specific heat kJ/kilogram and degree (at 15 ° C)||Heat of vaporization kJ/kilogram (at 20 ° C)|
|CO2||-56 (at 5 atm)||-78.5 (sublimes)||0.832||147|
|CH4||-182.5||-161.5||2.210||510 (at -161.6 °C)|
The figures in the preceding table clearly demonstrate how superior water vapor is compared to the other three major greenhouse gases when it comes to storing and transporting matter and energy around the globe. Water vapor is also many times more abundant in the atmosphere than the other gases (more than 70 times compared to CO2 if you compare the concentrations and maybe 3000 times more if you compare their CO2 equivalents). Water as ice also has a comparatively high heat of melting (abt. 334 kJ/kilogram).
Since water is so overwhelmingly abundant on Earth in the oceans (containing about 1 400 000 000 cubic kilometers or about 96.5% of all Earth water while water in the atmosphere is about 0.001% according to US Geological Survey) they have an overall stabilizing role primarily in the H2O and CO2 cycles for the global temperature. In the atmosphere, however, the large contents of N2 and O2 (abt. 78% and 21% respectively) do not play such an important role since these gases (and Ar) do not absorb important amounts of solar radiation in comparison with the greenhouse gases.
A comprehensive and environmentally sustainable solution of the problem of how to set bounds to the global warming needs to consider the cycles of the greenhouse gases and of their elements. The solution has to work with the cycles and must not act against them.
Water in its various phases in the atmosphere is the major factor that determines the global warming and the climate. It also holds the key to the solution of that problem.
Remark: Stratospheric Ozone (O3) is formed and regenerated in the Ozone-Oxygen cycle and considered to be a fairly strong greenhouse gas.