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Here is a compilation of term papers on ‘Greenhouse Gases’ for class 9, 10, 11 and 12. Find paragraphs, long and short term papers on ‘Greenhouse Gases’ especially written for school and college students.
Term Paper on Greenhouse Gases
Term Paper Contents:
- Term Paper on the Discovery of Greenhouse Gases
- Term Paper on Infra-Red Radiation and the Greenhouse Effect
- Term Paper on Greenhouse Gases, Natural and Anthropogenic
- Term Paper on the Properties of Greenhouse Gases
- Term Paper on Individual Greenhouse Gases
- Term Paper on Ozone Layer Depleting Gases
Term Paper # 1. Discovery of Greenhouse Gases:
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The Earth is surrounded by a layer of gases, known as the atmosphere. Hot solar beams travel through atmosphere and reach the Earth. These beams make the Earth warm, and heat from the earth travels back into the atmosphere. There are some gases in the atmosphere which trap the heat escaping from the Earth and stop it from traveling back into space.
The discovery of atmospheric gases, with high heat absorption capacities, long life, and their increasing presence due to industrialization resulting in global temperature increase has paved the way for the current hype on global warming, and its disastrous effect on climate.
Nearly two centuries ago, in 1827, Jean Baptiste Joseph Fourier, a famous French mathematician was the first to find that some of the gases in our atmosphere behave in a manner similar to a glasshouse or green-house, by allowing sunlight but preventing the solar heat radiating back in the outer space. These heat absorbing gases which cause a rise in atmospheric temperature are known as greenhouse gases.
John Tyndall, a British physicist in 1850’s, found that the heat absorption capacity of carbon dioxide, methane, water vapor and few other gases is enormous. They constitute less than 1% of the atmosphere, but their superior heat absorption capacity keeps the earth warm. Nitrogen and oxygen, which form 99% of the dry air, do not have the capacity to absorb heat.
Greenhouse gases make the Earth warm, and without that it would be too cold for living things, such as plants and animals. Naturally occurring greenhouse gases follow the natural cycles of absorption and emission. For example, carbon dioxide, a major greenhouse gas is formed and absorbed by natural ‘carbon cycle’.
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Carbon cycle maintains the same level of carbon dioxide in the atmosphere. However, man-made greenhouse gases are being produced everyday by transport systems, power generation and other manufacturing industries. These industrial emissions due to human activities are known as anthropogenic greenhouse gases.
Large amount of anthropogenic gas emissions makes the carbon cycle unbalanced and results in higher residual content of greenhouse gases in the atmosphere. The larger is the quantity of greenhouse gas in the atmosphere, the higher is the temperature rise.
Term Paper # 2. Infra-Red Radiation and the Greenhouse Effect:
The amount of energy emitted by radiation at temperature T is given by the Stefen-Boltzmann equation modified for the effects of emissivity, e, as follows:
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E = ex. T 4
Where σ = Stefan – Boltzmann constant = 5.67 × 10-8 W m-2 K-4
The variation of emissivity with wavelength is small for solid objects and is almost equal to 1.0 or more than 0.90 for various types of the Earth’s surface. However, he emissivity of gases varies over a wide range. Each gas absorbs radiant energy over a narrow wavelength range, called spectral absorption lines.
Normally these lines are grouped together as absorption bands. The location and the absorbing capacity depend on the molecular structure of the gas. With the increase in the amount of absorbing gas, its temperature, and the total atmospheric pressure, these bands are broadened and the amount of absorption increases.
The atmosphere is highly absorbent to infra-red radiation band due to the effects of water vapor, carbon dioxide and other trace gases. The opaqueness of the atmosphere to infra-red radiations, relative to its transparency to short wave visible spectrum, is commonly referred to as the ‘greenhouse effect’. The gases showing opaque behavior to infra-red radiation through absorption are called greenhouse gases.
Term Paper # 3. Greenhouse Gases, Natural and Anthropogenic:
Some of the greenhouse gases like carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), belong to both natural and anthropogenic origins, while others like moisture (H2O) & ozone (O3), are of natural origin. The atmospheric water vapor (H2O) also makes a large contribution to the natural greenhouse effect but it is thought that its presence is not directly affected by human activity.
Unlike other GHGs, moistures do not have the anthropogenic origin. Hence there is no enhanced greenhouse effect due to non-existent anthropogenic moisture in the atmosphere. Other gases like, sulfur dioxide (SO2) chlorofluorocarbon (CFCs) do not occur in the nature, but are of only anthropogenic(man-made) in origin.
Shortwave solar radiation can pass through the clear atmosphere relatively unimpeded. Long wave infra-red radiation, on the other hand, is emitted by the warm surface of the Earth and is absorbed partially and then re-emitted by a number of trace gases (particularly water vapor and carbon dioxide, which are present in the cooler atmosphere above). It is necessary to distinguish between the “natural” and a possible “enhanced” (formed due to anthropogenic) greenhouse effect.
The natural greenhouse effect i.e., the greenhouse gases produced by natural cycles, can cause the mean temperature of the Earth’s surface to rise up to about 33° C. Natural greenhouse effect creates a climate in which life can thrive and sustain. Without the heating effect of natural greenhouse gases, the Earth would be a very frigid and inhospitable place.
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However, an enhanced greenhouse effect refers to the possible increase in the mean temperature of the Earth’s surface above and beyond that occurring due to the natural greenhouse effect. The large amount of greenhouse gases in the atmosphere beyond that due to natural process, belong to the anthropogenic origin. Increase in global warming would probably bring other, sometimes deleterious changes in climate, such as, changes in precipitation, storm patterns, and the level of the oceans.
According to the Intergovernmental panel on Climate Change (IPCC), a joint project of the World Meteorological Organization and the United Nations Environment Program, if the carbon dioxide in the atmosphere continues to rise, the world will warm up by 2.5° F to 10.4°F (1.4 to 5.8°C) by the end of 21st century.
With a global temperature rise of 1.4°C, there would not be a major problem due to climatic changes. However if the temperature goes up to the highest level of 5.8°C, there would be a dramatic change in climate with disastrous consequences across the world.
The greenhouse effects of major greenhouse gases (GHGs) include following:
i. Water Vapor → causes ~ 36-70% of the GHG effect (not including cloud)
ii. Carbon Dioxide (CO2), → causes~ 9-26% of GHG effect
iii. Methane (CH4) → causes ~4-9% of GHG effect
iv. 0zone (O3) → causes ~3-7%.of GHG effect
Other gases contribute very small fractions of the greenhouse effect. However, in the recent decades there has been an increasing concentration of Nitrous Oxide (N2O) as a result of human activities, such as, the use of nitrate fertilizer in agriculture.
The atmospheric concentration of CO2 and CH4 has increased by 36% and 148% respectively since the beginning of the industrial revolution in the mid-1700s. The present CO2 levels are considerably higher, than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice core. Also almost all the increase is due to human activities.
Term Paper # 4. Properties of Greenhouse Gases:
The major properties of greenhouse gases, their origins and sinks, and the effects on global warming are tabulated in Table 5.1.
1. Radiative Forcing:
This is a measure of greenhouse effect (global warming) of the greenhouse gas, and is proportional to its concentration in the atmosphere. Molecule for molecule, methane is a more effective greenhouse gas than carbon dioxide, but its concentration is much smaller so that its total radiative forcing is only about a fourth of that from carbon dioxide.
The estimated average radiative forcing figures for greenhouse gases in 2005 are as follows:
CO2 = 1.7W/sqm,
CH4 = 0.5 W/sq.m
N2O = 0.15 W/ sq. m
Halocarbons -0.4 W/sq.m
2. Global Warming Potential (GWP):
The Global Warming Potential (GWP) is used within the Kyoto Protocol as a measure for the climatic impact of emissions of different greenhouse gases. A GWP value is defined over a specific time interval, so the length of this time interval must be stated to make the value meaningful. For example, methane has a GWP of 72 over 20 years, but a lower GWP of 25 over 100 years. This is because it is very potent in the short-term but then breaks down to CO2 and water in the atmosphere in the longer the period.
GWP is based on a number of factors, including the radiative efficiency (heat-absorbing ability) of each gas relative to that of carbon dioxide, as well as the decay rate of each gas (the amount removed from the atmosphere over a given number of years) relative to that of carbon dioxide.
It is a relative scale which compares the gas in question to that of the same mass of carbon dioxide, whose GWP is by definition equals to 1. A GWP is calculated over a specific time interval and the value of this must be stated whenever a GWP is quoted or else the value is meaningless.
GWP is defined by the IPCC as the ratio of the time-integrated radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas:
Where,
The term TH is the time period which over value is integrated. The choice of the time horizon depends on whether to emphasize shorter-term processes (e.g., responses of cloud cover to surface temperature changes) or longer-term phenomena (such as sea level rise) that are linked to sustained alterations of the thermal budget (e.g., the slow transfer of heat between, for example, the atmosphere and ocean). In addition, if the speed of potential climate change is of greater interest rather than the eventual magnitude, then a focus on shorter time horizons can be useful.
The term ax is the radiative efficiency due to a unit increase in atmospheric abundance of the gas (i.e., Wm-2 kg-1) and [x(t)] is the time-dependent decay in abundance of the substance following an instantaneous release of it at time. The radiative efficiencies ax and ar are not necessarily constant over time. The time horizon plays a role in the GWP values.
The parties to the UNFCCC have also agreed to use GWPs based upon a 100 year time horizon. The GWP is actually calculated in terms of the 100 year warming potential of a kilogram (kg) of a gas relative to that of a kilogram of CO2.(tab.3.1). According to the IPCC, GWPs typically have an uncertainty of ±35 percent.
The absorption of infra-red radiation by many greenhouse gases varies linearly with their abundance. A few important ones display non-linear behavior for current and likely future abundances (e.g., CO2, CH4, and N2O). For those gases, the relative radiative forcing will depend upon abundance and hence upon the future scenario adopted. Since all GWP calculations are a comparison to CO2, which is non-linear, all GWP values are affected.
Under the Kyoto Protocol, the Conference of Parties decided (decision 2/CP.3) that the values of GWP calculated for the IPCC Second Assessment Report are to be used for converting the various greenhouse gas emissions into comparable CO2 equivalent when computing overall sources and sinks.
The GWP has been subjected to many criticisms because of its formulation, but it has retained some favor because of the simplicity of its design and application, and its transparency compared to proposed alternatives.
3. Carbon Dioxide Equivalent:
Carbon dioxide is the major anthropogenic and natural greenhouse gas, which plays a key role in global warming. The effect of other gases on global warming are thus evaluated in comparison to carbon dioxide as GWP.GWP itself is a measure for comparing the global warming potential of various greenhouse gases in comparison to carbon dioxide. Carbon dioxide equivalents are commonly expressed as “million metric tons of carbon dioxide equivalents (MMTCO2Eq).”
The carbon dioxide equivalent for a gas is derived by multiplying the million metric tons of the gas by the associated GWP (8), as follows:
MMTCO2Eq = (million metric tons of a gas) × (GWP of the gas)
Carbon dioxide equivalents provide a universal standard of measurement against which the impacts of releasing (or avoiding the release of) different greenhouse gases can be evaluated.
As there is no possibility of directly influencing atmospheric water vapor concentration by anthropogenic sources, hence the GWP-level for water vapor is not calculated.
4. Global Temperature Change Potential (GTP): New Metrics for GWP:
Two new metrics, based on a simple analytical climate models have been proposed for global warming potential (GWP).
These new metrics are:
(i) Global Temperature Change Potential, which is the temperature change at a given time due to a pulse emission of a gas (GTPP);
(ii) Global Temperature Change Potential due to Sustained Emission Change, which is the temperature change due to a sustained emission change (hence GTPS).
Global Temperature Change Potential (GTP) goes further than GWP and integrated RF in describing the effects of emissions. It estimates the change in global mean temperature for a selected year in the future. Both GTPP and GTPS are calculated relative to the temperature change due to a similar emission change of a reference gas, which is ubiquitous carbon dioxide.
GTP is based on RF. However GTP calculation is more complex because it calculates climate response and not just radiative forcing. GTP accounts for Earth’s thermal inertia, i.e., the lag between when the emissions occur and when they cause warming. The calculation takes into account also the Earth’s climate sensitivity rather than simple radiative forcing calculations. It is more useful for policy makers to know what the actual temperature change will be than only the amount of energy that has been added to the system.
When compared against an upwelling-diffusion energy balance model that resolves land and ocean and the hemispheres, GTPP shows poor performance (except for long-lived gases) but GTPS shows good performance, for gases with a wide variety of lifetimes. Also for time horizons in excess of about 100 years, the GTPS and GWP produce very similar results, indicating an alternative interpretation for the GWP.
GTP can be used to express future climate responses to current aviation emissions. As with GWP, the chosen time horizon greatly influences the results. Short time horizons include the warming due to short-lived emissions, whereas longer time horizons exclude those effects.
5. Life Span of GHGs in Atmosphere:
The longer a greenhouse gas stays in the atmosphere, the more its cumulative heating effect. Although the GWPs are calculated on a 100 years basis, lifetime becomes an important parameter for the longer term heating effect.
Carbon dioxide has a long lifetime 100 years. However it remains in the atmosphere for several thousand years, but the impact on global warming is reduced to less than one quarter of its original impact after the first 100 years. The life span of nitrous oxide is 114 years. In contrast, both methane and HFCs are quickly removed from the atmosphere due to their relatively short atmospheric lifetimes of around 10 years. As a major emission, the long lifetime of CO2 means a significant commitment for climate change, long into the future.
6. Climate Impact:
The total quantity released is as important as the GWP in calculating the real environmental impact.
IMPACT = INDEX × QUANTITY
Despite the low GWP of CO2, the enormous quantities emitted and its long lifetime means that it has a far greater impact on climate than any other greenhouse gas. Currently, CO2 emissions contribute 64% of the total greenhouse gas emissions and the figures are still rising.
7. Feedbacks:
One of the most pronounced feedback effects relates to the evaporation of water. Warming by greenhouse gases, such as, CO2 will cause more water to vaporize into the atmosphere. Since water vapor itself acts as a greenhouse gas, the atmosphere warms further; causing more water vapor formation, and the process continues until a new dynamic equilibrium between water/vapor is reached. This results in a larger greenhouse effect than that due to CO2 alone.
Although this feedback process causes an increase in the absolute moisture content of the air, the relative humidity stays nearly constant or even decreases slightly because the air is warmer. This feedback effect can only be reversed slowly as CO2 has a long average atmospheric lifetime.
Term Paper # 5. Individual Greenhouse Gases:
The annex A of the Kyoto Protocol, a UN convention on climate change, includes the following greenhouse gases in the list:
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
Hydro fluorocarbons (HFCs)
Per fluorocarbons (PFCs)
Sulfur hexafluoride (SF6)
Ozone is covered by Montreal Protocol, hence omitted. Kyoto Protocol makes it obligatory for the signatory countries to control emissions of these gases to certain permissible limit. The properties of greenhouse gases are given in tab.5.1.
i. Carbon Dioxide:
The original atmosphere was that due to carbon dioxide from the volcanic emissions. It is only through the evolution of plant life, which began to take in carbon dioxide and give up oxygen that the earth’s atmosphere changed to one containing mostly oxygen, with a small share of carbon dioxide.
However, burning of fossil fuels, led to an increase in carbon dioxide from 280 ppm, a stable figure before industrialization, to 367 ppm in recent times. The net effect is a high rate of rise in the atmospheric carbon dioxide, which if not reduced, can lead to carbon dioxide concentration figures in the range of 490 to 1200 ppm in 2100, as predicted by Scientists at IPCC.
An important function of carbon dioxide is to sustain plant life through formation of carbohydrates by photosynthesis.
This is a biochemical process using light energy to make sugar from CO2, and H2O, while releasing O2 as per the following chemical reaction:
6CO2 + 6H2O (+ light energy) = C6H12O6 + 6O2.
This is the source of the O2 we breathe, and thus, a significant factor in the concern about deforestation. This process occurs in plants and some algae (photo planktons). This reaction doesn’t directly need light in order to occur, but it does need the products of the light reaction (ATP and another chemical called NADPH). The dark reaction takes place in the storma involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar. Stroma is a chlorophyll-containing plastid found in algal and green plant cells.
Another sink for CO2 is the ocean. Scientists felt that the ocean being a sink for carbon dioxide, would absorb the extra carbon dioxide. However, Scripps Institute of Oceanography found that the carbon dioxide absorption capacity of sea water is limited. A unique feature of carbon dioxide gas is the long life span of about 100 years in the atmosphere.
The cascading effect of increasing carbon dioxide through accumulation over 100 years would lead to an alarming rise in global atmospheric temperature. The long life of carbon dioxide, also means that even if we don’t burn fossil fuel for next 100 years, the present level of carbon dioxide would remain at the same level in 2100.
According to IPCC, in order to stabilize the carbon dioxide level in the atmosphere at 450 to 1000ppm, global use of coal, oil, and gas will have to be reduced to below the level at 1990, and continue to decrease steadily thereafter to a small fraction of whatever they are today.
Other Greenhouse Gases:
Although their levels in the atmosphere are much lower than that of CO2, gases like methane and fluorinated gases are also potent greenhouse gases.
ii. Methane:
Methane not only absorbs infra-red radiation, but also affects troposphere & stratospheric ozone. Methane on burning produces carbon dioxide. Although methane has higher global warming potential compared to carbon dioxide, due to its lower life (1/10th of CO2) and concentration its global warming effect is much less than that of carbon dioxide. Sinks for methane includes reaction with OH, and microorganisms in soil.
Although methane (“marsh gas”) is released by natural processes (e.g. from decay occurring in swamps), human activities may now account for over one-half of the total. The sources include, growing rice in paddies, burning forests and in raising cattle. In raising catties, the fermentation in their rumens produces methane that is expelled — collectively adding an estimated 100 million tons a year to the atmosphere. It was reported that some plants naturally release methane to the atmosphere. On reexamination, it was found that methane emissions from plants are negligible and do not contribute to global climate change.
The burning of the tropical rain forest adds to the atmospheric methane budget. The methane concentration in the atmosphere is presently some 1.8 ppm and is growing at a rate of 1% per year. Although this concentration is far less than that of CO2, methane is 30 times as potent a greenhouse gas and so may now be responsible for 15-20% of the predicted global warming.
iii. Nitrous 0xide (N2O):
Nitrous oxide is produced by burning biomass, fossil fuels, and from nitrate fertilizers. Nitrous oxide absorbs infrared radiation and affects stratospheric ozone. Nitrous oxide has a very long life of 114 years. Also its global warming potential is very high, in the regions of 275 (for 20years), 296(100 years) and 197 (in 500 years) when compared to that of CO2, which has a GWP of 1 (tab.3.1).
iv. High GWP Gases- Fluorinated Gases:
There are three major groups or types of high GWP fluorinated gases hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). All of them are of anthropogenic origin.
a. Hydrofluorocarbon (HFCs):
HFC’s stand out as a good choice for refrigeration due to their ODP(Ozone Depletion Potential) of 0, but have a high GWP of 1200 and an atmospheric lifetime of 16 years. Pentafluoroethane (HFC- 125) degrades in the atmosphere to CO2 and HF by reaction with naturally occurring hydroxyl radicals. The atmospheric lifetime is estimated to be 40.7 years. Pentafluoroethane has no effect on stratospheric ozone since it contains neither chlorine nor bromine. However, Pentafluoroethane has a global warning potential of 2800 relative to CO2 at 100 years.
b. Perfluorocarbons (PFCs):
A PFC (perfluorinated carbon) compound is defined as a compound containing carbon and fluorine only. Perfluorocarbons are highly volatile, linear, branched chain or cyclic per-fluorinated carbons (C1 up to C6, fully saturated).This definition covers the most common commercial PFC gases and liquids with boiling points up to 56°C even though there are other PFC compounds, mainly used in closed system heat transfer applications.
The GWP and Lifetime data of some PFCs are as follows:
PFC gases and liquids are traditionally used in several electronic industry processes ranging from semiconductor front-end manufacturing, IC-component quality control testing, to direct contact dielectric cooling of power electronics assembly. With the phase-out of ozone-depleting substances, PFCs have been introduced. However, PFCs are only selected for “high-end” performances, where system efficiency and worker safety are mandatory due to extremely high price (>60 Euro/1).
c. Sulfur Hexafluoride (SF6):
Sulfur hexafluoride (SF6) is an excellent dielectric gas, which is used for high and medium voltage switchgear. It is chemically inert, gaseous even at low temperature, nonflammable, nontoxic, non-corrosive. Its combined chemical, thermal and electrical properties allow many advantages to be achieved.
The global warming properties of SF6 include the following:
*GWP = 24,900(100 years); *Lifetime = 3,200 years
SF6 is present in air in its inert form.
Ecological limits dictate that to avoid dangerous climate change we must reduce total greenhouse gas emissions below 1990 levels by a minimum of 50% within the next fifty years, and 60-80% in the next century.
Other Minor Gases:
Carbon Monoxide (CO):
This is an unstable gas, emitted by industries and transports, while burning carbon containing fuels. It reacts with oxygen in air to produce CO2, and is also absorbed by soil.
Sulfur Dioxide:
It originates from volcanic eruptions and is also produced by burning coal and biomass. The sinks for SO2 include dry and wet depositions and reaction with moisture. It forms aerosols, which scatter solar radiation.
Term Paper # 6. Ozone Layer Depleting Gases:
The Ozone layer in the stratosphere filters the harmful UV-rays from solar radiation before it reaches to Earth’s atmosphere. However there are several industrial gases, which are found to be responsible for depleting ozone in the ozone layer. The major ozone depleting gases are CFC, HCFC and HFC.
Ozone depletion capacity of a gas is expressed by the Ozone Depletion Potential (ODP), and depends like the GWP on the atmospheric lifetime of the gas (measured in years). Atmospheric lifetime is a critical factor, as it determines how long the substance in question can continue to cause damage.
a. Chlorofluorocarbons (CFCs):
These are synthetic gases in which the hydrogen atoms of methane are replaced by atoms of fluorine and chlorine (e.g., CHF2Cl, CFCl3, CF2Cl2). CFCs absorb infrared and dissociate and react with ozone in stratosphere. CFCs have long life spans from 45 years for CFC11, through 100 (CFC12), 640 (CFC13) to 1700 (CFC1s).
Global warming potential (GWP) for CFCs have a range of 4500 to 10,200 when compared to carbon dioxide. Their long lifetime means that they can be transported slowly to the stratosphere. Although CFCs were banned within a few years of the Montreal Protocol in 1987, their long lifetime means that it will take many more years before their atmospheric concentrations level out and then decrease.
b. HCFC:
HCFC’s are an improvement over CFCs with a GWP of 1500, an ODP of 0.07 and an atmospheric lifetime of 15 years. As a refrigerant, they still fall short of environmental safety.
Steps to Reduce Halocarbon Generation:
Unlike other GHGs, the halocarbons are totally man-made products, hence completely avoidable with the development of suitable alternative chemicals.
Most HCFC’s are now banned in developed countries (Montreal Protocol and EU Regulation). They are still allowed in developing countries. HFC/PFC/SF6 emissions present a real danger to the planet.
Eliminating the use of HFCs/PFCs/SF6 is one of the easiest ways for advanced nations to accomplish their commitments under the Kyoto Protocol and for companies to demonstrate corporate environmental leadership. Environmentally safer, cost effective, technically reliable alternatives to HFCs/PFCs exist in virtually all applications. There are companies in many countries that are ready to provide these alternative technologies.