we talk about green house gases...We keep hearing about them all the time , without perhaps understanding their significance and its impact on climate change.
So what are GHG’s ?
Gases that trap heat in the atmosphere are called greenhouse gases. They are carbon dioxide , methane ,nitrous oxide and other fluorinated gases ….
How long do the gases stay in the atmosphere? - Each of these gases can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years. All of these gases remain in the atmosphere long enough to become well mixed, meaning that their measure in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.
Some gases are more effective than others at making the planet warmer and as they say, "thickening the Earth's blanket" .For each greenhouse gas, a Global Warming Potential (GWP) was developed to allow for comparisons of the global warming impacts of different gases. Specifically, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO2). Gases with a higher GWP absorb more energy, per kilo emitted, than gases with a lower GWP, and thus contribute more to the warming the Earth. So a GWP of NO2 is estimated to be about 250 times that of CO2 , which means that Nitrous oxide has that many times the heating potential of Carbon dioxide in a period of time . Second important consideration , is the residence time of a particular gas in the atmosphere . Carbon dioxide has a very long residence time , lasting upto thousand years and so are many fluorinated gases, while a methane and nitrous oxide has lower residence time , lasting upto, about twenty years and 100 years respectively . Therefore, the longer the residence time and the higher the warming potential of a gas , the bigger the issue .
Now let us look at each of these gases in a bit of detail.
Carbon dioxide is the most prevalent of emitted green house gases ( at 68% ). Carbon dioxide , enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), and through solid waste, trees and other biological materials, and also as a result of certain chemical reactions (example say, in manufacture of cement). Carbon dioxide is removed from the atmosphere (or "sequestered") when it is absorbed by plants as part of the biological carbon cycle.
Methane is another important green house gas and is second only to carbon dioxide with 16% of the share . Methane has a global warming potential of 56 and is formed naturally by the bacterial decomposition of organic matter under oxygen-free conditions. Because of various types of human activity, emissions of methane have roughly doubled in the last 2 decades. Rice cultivation, cattle breeding, emissions from coal mines and the leakage of fossil gas, represent significant anthropogenic sources around the world, as do the treatment of wastewater and organic waste. The pre-industrial concentration of methane is estimated to have been 0.7 parts per million or ppm. Today’s level (at 2011 estimates ) is more than twice as high, about 1.8 ppm. The life of methane in the atmosphere is relatively short, on an average only 10–15 years.
Nitrous oxide is a greenhouse gas which is emitted during agricultural and other land use, Also due to industrial activities, combustion of fossil fuels and solid waste; as well as during treatment of wastewater. Denitrification is the main source of nitrous oxide in the atmosphere. This process, which is carried out by micro-organisms, occurs naturally in the soil. However, the more nitrogen is made available to plants by adding it in the form of fertilizer or through the deposition of airborne nitrogen, the more nitrous oxide is formed. Another source of nitrous oxide emissions is all sorts of combustion. During the combustion process, small amounts of N2O are formed in addition to the “ordinary” nitrogen oxides (N O and NO2). This amount depends largely on the combustion conditions. Nitrous oxide is a greenhouse gas whose pre-industrial level is estimated to have been 270 ppb (parts per billion). The level in 2011 was 324 parts per billion, an increase of 20 percent. About a third of the nitrous oxide emitted today, are caused by humans. Nitrous oxide has a long residence time in the atmosphere, with an average of about 120 years, and also a very high warming potential at 280 ,which makes it doubly potent .
Fluorine compounds The greenhouse gases described so far occur naturally in the atmosphere.
This does not apply to the group of synthetic fluorine compounds, which in many cases are very long-lived and potent greenhouse gases. Their large heating effect, per molecular weight, is due to their ability to absorb radiation in a previous fully transmissive part of the infrared spectrum.
The most familiar substances in this group are the chlorofluorocarbons (CFC gases, known as CFC’s), which have mainly attracted attention because of their ability to break down the stratospheric ozone. CFC gases are also powerful greenhouse gases. Measured per molecule, some of them are tens of thousands of times more effective than carbon dioxide. CFC gases are however being phased out globally. Other substances in this group are so-called f-gases, which have significant greenhouse effects and include: HFC's, which are similar to CFCs but do not contain chlorine and therefore do not affect the ozone layer. Used as a replacement for CFCs in many applications. They are not as long-lived in the atmosphere as CFCs and not as powerful in their greenhouse effect. Sulphur hexafluoride (SF6), used in the electronics industry, for example. PFC's (also called fluorocarbons, FC's) emitted during alluminium production, but also used in the electronics industry. Since the released amounts of these substances are small, their contribution to the greenhouse effect is so far only a few percent, calculated over a hundred-year period. However, global emissions are increasing rather sharply, particularly of HFCs, and several of them have effects that last for a very long time – the mean residence time of SF6 in the atmosphere is estimated at 3,200 year.
Other elements which play a limited yet significant factor in heating of the atmosphere are Ozone and residual particulate matter .
Ozone in the stratosphere has made it possible for animals to live on land by preventing harmful 200–300 nm UV radiation from reaching the Earth's surface. The absorption of UV radiation by ozone, however, heats the air, disturbing air convection and creating a layered structure in the stratosphere hence is one of the so-called greenhouse gases. In the lower troposphere, photochemical reactions of air pollutants (hydrocarbons and nitrogen oxides) produce ozone as well as other atmospheric oxidants such as hydrogen peroxide (H2O2), organic peroxides, and peroxyacyl nitrates that result in what is called photochemical smog. Daytime ozone concentrations often exceed 0.1 ppmv in polluted air. Ozone and other oxidants promote oxidation of sulfur dioxide (SO2) and nitrogen oxides into sulfuric and nitric acids, respectively, bringing about the occurrence of acid rain.
Ozone is being used in the field of water treatment, disinfection, decolorization, deodorization, organic synthesis, materials testing, dry etching and cleaning processes in semiconductor industries, and other industrial areas. The advantages of using ozone over other chemicals are: its strong oxidizing power, its clean nature leaving only oxygen after the treatment, and electrical generation at the site.Ozone is also emitted from germicide lamps, copy machines, printers, welding, and other industrial processes. The working environment criteria for ozone are set at 0.05–0.1 ppmv in most countries. Ozone is a colorless gas at ambient temperature and pressure and has a characteristic odor even at very low concentrations. It has a strong oxidizing ability that is hazardous to plants and animals, and is unstable especially at higher concentrations. Monitoring of ozone is therefore important from the viewpoint of workplace health and hygiene. Among the substances that could have significant impact as greenhouse gases, ozone is the most short-lived. Its retention time in the troposphere is weeks or a month. Ozone in the lower troposphere acts as a greenhouse gas and the level has risen an average of 1–2 percent per year in recent decades. The increase occurred primarily across North America and Europe, so the climate effect in this case is regional. One special effect in the context of climate change is due to emissions of nitrogen oxides from aviation in the upper troposphere, where most commercial aviation travel takes place. At this height nitrogen oxides cause extensive formation of ozone.
Monitoring of ozone concentration is thus indispensable for protection of both the local and global environment. Particles in the atmosphere also affect the radiation balance. Sulphate particles reflect incoming sunlight and hence reduce the amount of solar energy that reaches the Earth’s surface. Sulphate particles originate from sulphur dioxide emissions.
There are also carbon particles (“black carbon”) in the air. These can both absorb heat and reflect incoming light. Their net effect on climate is therefore difficult to assess. Particles of black carbon can both absorb heat and reflect incident light. Particles also have an effect on the environment by forming condensation nuclei for water vapour in the atmosphere, which can affect cloud formation and precipitation. Unlike greenhouse gases, the residence time of particles in the air is short, about two weeks. The net effect of particles is difficult to assess and contributes to a high degree of uncertainty, but has been estimated by the IPCC to be somewhere between -0.1°C and -1.9°C.
To summarize, - Global carbon emissions from fossil fuels have significantly increased since the 1900’s. Since 1970, CO2 emissions have increased by about 90%, with emissions from fossil fuel combustion and industrial processes contributing, about 78%, of the total greenhouse gas emissions increase from 1970 to 2011. Agriculture, deforestation, and other land-use changes have been quite significant as well ,as the second-largest of contributors. Emissions of non-CO2 greenhouse gases have also increased significantly since 1900. The G20 nations contribute to 80% of GHG’s in the world on an ongoing basis .Only the share amongst them has altered over time .The G20 in turn, contribute to 90% of world’s GDP . So It is easy to see the connection between growth , human activity and rise in emissions.
The question is what do we as humans do, about reducing the emissions , bringing down the earth’s temperature and avert a climate change crisis . We are running out of time and running out of easy options .
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