Thursday, January 28, 2010
Global Warming – Understanding Greenhouse Gases and their Effects
In my previous GW posts I have briefly explained the greenhouse gases and how they affect our atmosphere. In this post we will take a wider look at these gases, sources, their effects and what can we do to reduce their generation.
Greenhouse Gases are primarily those gases in our atmosphere that does not allow some of the sun’s heat reflected back from earth’s surfaces to go out into the outer space. They trap the heat and in turn heat up the earth’s surface. However greenhouse effect is otherwise a natural process and we will not have life on Earth but for these gases. What makes them alarming now is the rate of increase of these gases in our atmosphere that is solely due to man-made actions. Therefore overall the earth is heating up at an accelerated rate that will outpace the natural cooling processes. There are many visible and latent effects of GW on our planet and the point to be noted is that it is more like a chain reaction where one thing leads to another so each factor of GW in turn affects another and it is continuously accelerating at a rate that is already beyond our control. There are many gases that have greenhouse effect but only few matters to us. Let’s compare them first and then we will look at them in details. There are five major greenhouse gases in our atmosphere; water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and chlorofluorocarbons (CFCs). Some experts erroneously claim ozone too as a greenhouse gas, and though the ozone hole above Antarctica has been much in news ozone has a different affect on our atmosphere and its subsequent implications to GW that I will explain later.
To compare the five major greenhouse gases we will compare them first in terms of potency and longevity. The first scale is often termed as ‘GW Potential’ (GWP). GWP is a comparison efficiency of a gas in terms of greenhouse potentiality as compared to CO2 over a time span of 100 years. A gas with 10 GWP is 10 times more efficient at retaining heat than CO2 over a 100 year of time period. The other way to measure a greenhouse gas potential threat to our atmosphere is the average time (longevity) they would remain in the atmosphere once they are emitted. No matter what we do now, the gases that have already been emitted and are already in the atmosphere, will take hundreds of years to dissipate adequately. Now let’s take a closer look at the gases themselves.
Carbon Dioxide (CO2): This is naturally present in the atmosphere and though overall only constitutes about .036% of the entire atmosphere it has the highest concentration in our atmosphere of all the greenhouse gases and creates the greatest GW effect. As per estimates, CO2 alone is responsible for around 55 – 60% of the total greenhouse effect. Natural CO2 is due to the exchange between the atmosphere and life through the processes of photosynthesis and respiration. The increase in CO2 concentration in our atmosphere is solely due to man-induced reasons primarily burning of fossil fuels, coal, etc for energy production, and modern modes of transportation like car, aircraft, ships, etc. Therefore we generally talk in terms of carbon footprints of a nation or of an individual for measuring its effect on GW. Massive deforestation is also a reason as we are cutting down trees that otherwise would have reduced CO2 percentage by photosynthesis. GWP of CO2 is obviously 1 and its average life is around 100 years. Current estimate of world’s annual CO2 production due all reasons (including respiration & volcanic activities) is around 8 billion tons. Currently in the world 40% of all CO2 emissions are caused by power plants. These are burning coal, natural gas and diesel fuel. 33% of all the CO2 is produced from cars and trucks, etc. Internal combustion engines burning fossil fuel. Gasoline and diesel generate obscene amounts of CO2. Though only 3.5% of all CO2 emissions are released from aircraft ironically they leave their pollutants directly into the troposphere, which have a far more effective and immediate effect on GW. Arguably around 12% of all CO2 released into the atmosphere is related to buildings. This figure though slightly debatable is still an under-estimate. In newly constructed buildings, production of materials used in building and energy used during construction are the causes of CO2 emissions. In existing buildings the CO2 created by the energy upkeep of the building is the root of the emissions volume.
As of now the CO2 concentration in our atmosphere is close to 380 parts per million (ppm: for every one million air molecules there are 380 CO2 molecules) whereas the safe human limit is considered to be 350 ppm. At current rate of CO2 emission it is estimated that by 2030 we would reach a killing proportion of 500 ppm. The only way we can contain this ppm and perhaps in a long time bring it down is to minimize burning of fossil fuel and deforestation. Since CO2 is the largest contributor to GW we refer to it as carbon footprint. A country or a society and even individuals can be measured by their carbon footprints and there are ways, mostly in the way we live, what we eat and how we commute, etc by which we can bring it down to minimum. Most of these large scale changes can only be brought about by political will and green policies that have further ramifications on our existing industries. Most governments are under heavy pressure from the scientists and citizens to bring about radical policy changes whereas the industry and big money making corporate lobby the other way. Hence most governments are unable to take any measures that will have large impacts on the nation’s carbon footprint. The Copenhagen fiasco, Kyoto Protocol are the most recent examples. We have reached a stage where every human on earth has to do his or her bit and collectively reject energy guzzling projects and products. I will cover this aspect in details in a separate post as to what actions we each and the government can take to reduce carbon and other greenhouse gas footprints. What’s important to remember is that 98% of all CO2 emissions are related to energy production and 80% of these emissions become greenhouse gases.
Methane (CH4): By volume Methane comprises only 0.00017% of the entire atmosphere but in terms of GWP it is nearly 25 times stronger than CO2. It contributes to around 10% of the total greenhouse effect as per present concentrations. The primary anthropogenic sources are fossil fuel combustion, decomposition of organic materials from wetlands, rice paddy fields and livestock manure. We are releasing around half a billion tons of methane annually. Thankfully it doesn’t last longer than a decade after emission. Methane is also released from landfills, coal mines, and gas and oil drilling. Landfills produce methane as organic wastes decompose over time. Coal, oil, and natural gas deposits release methane to the atmosphere when these deposits are excavated or drilled. Over the last two centuries the methane concentration has increased by more than 150%. Recent studies show (a project where I am personally involved in the field) that due to GW the permafrost in the Polar Regions are thawing at an alarming rate releasing enormous amount of methane from the underlying organic materials that had remained frozen until now. This is an area requiring major field work in the years to come. Since most of the world’s paddy and rice fields are in India and China and cater to around half of world’s population, the increase in methane can also be directly attributed to our growing population that is estimated to reach a whopping nine and half billion by 2040.
Nitrous Oxide (N2O): Though .00003% of atmospheric volume, N2O has a GWP of 300 which makes it a significant greenhouse gas. It contributes to around 6% of the total greenhouse effect. The primary sources of N2O are fossil fuel combustion, soil fertilization, biomass burning, etc. Most of the nitrous oxide added to the atmosphere each year comes from deforestation and the conversion of forest, savanna and grassland ecosystems into agricultural fields and rangeland. Both these processes reduce the amount of nitrogen stored in living vegetation and soil through the decomposition of organic matter. The use of nitrate and ammonium fertilizers to enhance plant growth is another source of nitrous oxide. N2O doesn’t last longer than weeks but it is being continuously replenished by humans.
Chlorofluorocarbons (CFCs): CFCs are the only major greenhouse gases that do not occur naturally in our atmosphere. They come solely from human sources like production and use of foams, aerosols, refrigerants and chemical solvents. Though they are present in almost incalculable (miniscule) volume they are nearly 15K times more potent as a greenhouse gas relative to CO2. Due to this they contributed to around 24% of the total greenhouse effect during the last decade. CFCs typically take anywhere between 75 – 100 years to dissipate from the atmosphere.
Water Vapor (H2O): Water vapor happens to be the third most abundant gas in our atmosphere (after nitrogen and oxygen) and though in terms of man-induced greenhouse gas effects it does not have any significance since entirely all of its presence is caused by natural process of evaporation, etc it is a significant greenhouse gas (about which we actually can’t do much and we shouldn’t really). Water vapor varies in concentration in the atmosphere both spatially and temporally. The highest concentrations of water vapor are found near the equator over the oceans and tropical rain forests. Cold polar areas and subtropical continental deserts are locations where the volume of water vapor can approach zero percent. Water vapor redistributes heat energy on the Earth through latent heat energy exchange, it also creates rain and provides much of the fresh water for animals and it also helps to warm up Earth’s atmosphere.
Ozone (O3): It accounts for only 0.000004% of our atmospheric volume and it primarily provides a screen against the penetration of harmful ultraviolet radiation from Sun. Ozone layer extends into the stratosphere, typically from 10 to 50 km above the surface and it absorbs nearly 95% of the Sun’s UV radiation. Though it is still not understood clearly as how depletion of Ozone can give rise to GW since by itself it isn’t a greenhouse gas, it is speculated that it could have some effect after all. Ozone depletion is mainly caused by release of man-induced CFCs and the largest Ozone hole is found above Antarctica. It is theorized that since Ozone depletion would actually increase Sun’s UV radiation penetration and this can in some way heat up the earth’s surface and atmosphere. There is no scientific data based evidence yet to prove or disprove this theory.
As is evident from the above that all the harmful greenhouse gases are either being produced by man or their production rate has been increased due to direct and indirect action of human. I don’t think any climate scientist has so far made a connection but I have and I do connect this to our rising and bulging population. In most probability the population rise will never be curbed or reduced and we will keep growing year after year and to feed and survive for this ever increasing volume our actions will also keep generating more and more volumes of greenhouse gases. Perhaps there is no solution and perhaps there is… but what really defies my intelligence is that how we, human beings can be so absurdly illogical. We have the solution right in our hands but we won’t open our fists and look inside. For the first time in Earth’s history, a specie has become its own greatest enemy and for whom natural survival has become a problem that he needs to solve. Where will it all end, is a question we all can answer, what we really don’t know is WHEN?