The History Of Greenhouse Gases

Published Date: 02 Nov 2017

1.1 Introduction

Greenhouse gases (GHG) are those gases (e.g.CO2, CH4) present in the atmosphere which reduce the loss of heat into space and therefore contribute to increase global temperature which is detrimental to animal, plant and microorganism, create ozone hole in ozone layer. According to the International Panel on Climate Change (IPCC) report (2007), warming of the climate system is occurring at unprecedented rates and an increase in anthropogenic greenhouse gas concentrations is responsible for most of this warming. Methanogenic Achaea, bacteria, soil microorganisms contribute significantly to the production and consumption of greenhouse gases, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and nitric oxide (NO).

Human activities such as waste disposal and agriculture have stimulated the production of greenhouse gases by microbes. As concentrations of these gases continue to raise, soil microorganisms may have various feedback responses that accelerate or slow down global warming, but the extent of these effects are unknown. Understanding the role soil microorganism have as both contributors to and reactive components of climate change can help us determine whether they can be used to curb emissions or if they will push us even faster towards climatic disaster. Carbon dioxide is released largely from microbial decay or burning of plant litter and soil organic matter (Janzen 2004; Smith 2004b). Methane is produced when organic materials decompose in oxygen-deprived conditions, notably from fermentative digestion by ruminant livestock, stored manures and rice grown under flooded conditions (Mosier et al. 1998). Nitrous oxide is generated by the microbial transformation of nitrogen in soils and manures, and is often enhanced where available nitrogen exceeds plant requirements, especially under wet conditions (Smith & Conen 2004; Oenema et al. 2005). Agricultural greenhouse gas (GHG) fluxes are complex and heterogeneous, but the active management of agricultural systems offers possibilities for mitigation. Many of these mitigation opportunities use current technologies and can be implemented immediately.

Since the beginning of Industrial Revolution, concentrations of carbon dioxide, methane, and nitrous oxide have all risen dramatically because of human activities. Fossil fuel combustion, land-use change, increasingly intensive agriculture, and an expanding global human population are the primary causes for these increases. Other greenhouse gases found in our planet's atmosphere include water vapor, ozone, sulfur hexafluoride and chlorofluorocarbons. Emissions from the combustion of fossil fuels account for about 65% of the carbon dioxide added to the atmosphere. The remaining 35% is derived from deforestation and the conversion of prairie, woodland, and forested ecosystems primarily into less productive agricultural systems. Natural ecosystems can store 20 to 100 times more carbon dioxide per unit area than agricultural systems.

It has been estimated that global anthropogenic greenhouse gas (GHG) emissions from the livestock sector approximate to between 4.1 and 7.1 billion tones of CO2 equivalents per year, equating to 15-24% of total global anthropogenic GHG emissions (Steinfeld et al., 2006). The term ‘CO2 equivalent’ represents the total impact of a particular GHG in the atmosphere on heat retention, and the Global Warming Potential (GWP) for a particular GHG is the ratio of heat trapped by one unit mass of the GHG to that of one unit mass of CO2. While the GWP of CO2 is 1, the GWP for methane (CH4) and nitrous oxide (N2O) are x 23 and x 296 the GWP of CO2 when expressed over a 100 year time frame (IPCC, 2001). With livestock estimated to produce 9, 35-40 and 65% of the total anthropogenic emissions of CO2, CH4 and N2O respectively, effects on global warming can clearly be significant. While some more recent studies have suggested that these estimates are conservative, others propose that these percentages are too high (Goodland and Ahang, 2009; Pitesky et al., 2009). Most of the emissions of both CH4 and N 2O from livestock systems arise on the farm – CH4 primarily from rumen fermentation and N2O mostly from animal manures.

Algae, cyanobacteria, methanotrophs, photosynthetic bacteria, green bacteria, green purple bacteria and nitrifying bacteria are generally recognized as the most promising solution for reduction of Greenhouse Gases (GHG).

1.2 Greenhouse gases:

The Earth is wrapped in a blanket of air called the 'atmosphere', which is made up of several layers of gases. The sun is much hotter than the Earth and it gives off rays of heat (radiation) that travel through the atmosphere and reach the Earth. The rays of the sun warm the Earth, and heat from the Earth then travels back into the atmosphere. The gases in the atmosphere stop some of the heat from escaping into space. These gases are called greenhouse gases (GHG) and the natural process between the sun, the atmosphere and the Earth is called the 'Greenhouse Affect', because it works the same way as a greenhouse. Greenhouse gases trap heat and make the planet warmer. Industrialization has led to too much of a good thing, resulting in global warming. Any activity or policy that can reduce GHG emissions is a partial solution to global warming. But it's important to distinguish between the natural greenhouse effect and potential human impacts on it (the 'anthropogenic' greenhouse effect). Remember that, in the absence of the natural greenhouse effect, global temperatures would be too low to sustain life as we know it.

The Greenhouse gases are very important and are mainly:

Water vapor (H2O)

Carbon dioxide (CO2)

Methane (CH4)

Nitrous oxide (N2O)

Ozone (O3)

Fluorinated gases (F-gases)

2.1 Emission of greenhouse gases (GHG)

At the global scale, the key greenhouse gases emitted by anthropogenic and natural activities are:

Carbon dioxide (CO2) - Fossil fuel use is the primary source of CO2. The way in which people use land is also an important source of CO2, especially when it involves deforestation. Land can also remove CO2 from the atmosphere through reforestation, improvement of soils, and other activities.

Methane (CH4) - Agricultural activities, waste management, and energy use all contribute to CH4 emissions.

Nitrous oxide (N2O) - Agricultural activities, such as fertilizer use, is the primary source of N2O emissions.

Fluorinated gases (F-gases) - Industrial processes, refrigeration, and the use of a variety of consumer products contribute to emissions of F-gases, which include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).

2.2 Major source of greenhouse gases

Major sources of GHG emissions include transport, power generation and industrial activities that depend on fossil fuels, which release carbon dioxide and other greenhouse gases when they burn.

Deforestation is another major source, accounting for about one-fifth of all greenhouse-gas emissions from human activities. When forests are cleared or burned this releases carbon dioxide that had been locked away in the living plant material.

Agriculture is also a big source, and not only if forests are cleared to grow crops. Most fertilizers and pesticides are produced using fossil fuels. Large scale intensive agriculture produces high emissions as it depends heavily on these inputs and well as on fuel for mechanized farming and transport.

Landfills are one of the major sources of methane (CH4), a potent greenhouse gas with a global warming potential (GWP) ∼23 times higher than that of carbon dioxide (CO2). Although methanotrophs can be easily stimulated with the addition of nitrogenous fertilizers, biogenic production of nitrous oxide with a GWP ∼296 times higher than that of carbon dioxide, is also stimulated.

Farms are also a major source of a powerful greenhouse gas called methane, which is produced by bacteria that live in waterlogged rice fields and in the digestive tract of cows, which emit the gas when they burp.

Although these methane emissions are small compared to those of carbon dioxide from other sources, they are still important because methane has a far stronger warming effect. A single molecule of methane traps about 25 times more heat than one of carbon dioxide

3.1 Natural greenhouse effect

The atmosphere has a number of gases, often in tiny amounts, which trap the heat given out by the Earth. To make sure that the Earth's temperature remains constant, the balance of these gases in the atmosphere must not be upset. Methane makes up just 0.00017% of the Earth's atmosphere. However, it is an important greenhouse gas, with a much greater warming potential than CO2. Methane is generated through anaerobic decay of organic material. The amount of methane in the atmosphere is the result of a balance between production on the surface and destruction in the atmosphere. CH4 remains in the atmosphere for between 8 and 12 years. It's removed by being oxidized in the troposphere, first to carbon monoxide (CO) and finally to CO2 and hydrogen gas (H2).

3.2 Enhanced greenhouse affect

The greenhouse effect is not a new discovery. It was discovered by Joseph Fourier in 1824, experimented on by John Tyndall in 1858, and first reported quantitatively by Svante Arrhenius in 1896.Some of the activities of man also produce greenhouse gases. These gases keep increasing in the atmosphere. The balance of the greenhouse gases changes and this has effects on the whole of the planet. Burning fossil fuels - coal, oil and natural gas - releases carbon dioxide into the atmosphere. Cutting down and burning trees also produces a lot of carbon dioxide.

A group of greenhouse gases called the chlorofluorocarbons, - which are usually called CFCs, because the other word is much too long! - have been used in aerosols, such as hairspray cans, fridges and in making foam plastics. They are found in small amounts in the atmosphere. They are dangerous greenhouse gases because small amounts can trap large amounts of heat.

Because there are more and more greenhouse gases in the atmosphere, more heat is trapped which makes the Earth warmer. This is known as global warming. A lot of scientists agree that man's activities are making the natural greenhouse effect stronger. If we carry on polluting the atmosphere with greenhouse gases, it will have very dangerous effects on the Earth.

With more heat trapped on Earth, the planet will become warmer, which means the weather all over Earth will change. For example, summers will get hotter, and winters too. This may seem a good idea, but the conditions we are living in are perfect for life, and a large rise in temperature could be terrible for us and for any other living thing on Earth.

Climate change is already having impacts and these are set to increase, posing threats to vulnerable communities, infrastructure and ecosystems. These impacts include rising seas, changes to patterns of disease, risks of floods and droughts, heat waves and possibly more, stronger hurricanes.

Weather

The effects will be different throughout the world, some places will become drier and others will be wetter. Although most areas will be warmer, some areas will become cooler. There may be many storms, floods and drought, but we do not know which areas of the world will be affected. All over the world, these weather changes will affect the kind of crop that can be grown. Plants, animals and even people may find it difficult to survive in different conditions.

Sea levels

Higher temperatures will make the water of the seas and oceans expand. Ice melting in the Antarctic and Greenland will flow into the sea. All over the world, sea levels may rise, perhaps by as much as 20 to 40 cm, by the beginning of the next century. Higher sea levels will threaten the low-lying coastal areas of the world, such as the Netherlands and Bangladesh. Throughout the world, millions of people and areas of land will be at danger from flooding. Many people will have to leave their homes and large areas of farmland will be ruined because of floods. In Britain, East Anglia and the Thames estuary will be at risk from the rising sea.

Farming

The changes in the weather will affect the types of crops grown in different parts of the world. Some crops, such as wheat and rice grow better in higher temperatures, but other plants, such as maize and sugarcane do not. Changes in the amount of rainfall will also affect how many plants grow. The effect of a change in the weather on plant growth may lead to some countries not having enough food. Brazil, parts of Africa, south-east Asia and China will be affected the most and many people could suffer from hunger.

Water

Everywhere in the world, there is a big demand for water and in many regions, such as the Sahara in Africa; there is not enough water for the people. Changes in the weather will bring more rain in some countries, but others will have less rain.

3.3 In danger!

Plants & Animals

It has taken million of years for life to become used to the conditions on Earth. As weather and temperature changes, the homes of plants and animals will be affected all over the world. For example, polar bears and seals will have to find new land for hunting and living, if the ice in the Arctic melts. Many animals and plants may not be able to cope with these changes and could die. This could cause the loss of some animal and plant species in certain areas of the world or everywhere on Earth.

According to IPCC, the increase in global temperatures leads to drastic climatic changes. Higher global temperatures results in change in precipitation patterns, worldwide melting of ice and a rise in sea levels. Changes in average temperature can disrupt ecosystems (which are built on an interdependent chain of thousands of species). A rise in the sea-level could destroy the low-lying habitats of certain species. An example in this regard is the royal Bengal tiger, whose habitat (the mangroves in the Bay of Bengal in Asia) could be threatened by the rising sea level ("The Atlas of Climate Change: Mapping the World's Greatest Challenge").

People

The changes in climate will affect everyone, but some populations will be at greater risk. For example, countries whose coastal regions have a large population, such as Egypt and China, may see whole populations move inland to avoid flood risk areas. The effect on people will depend on how well we can adapt to the changes and how much we can do to reduce climate change in the world.

3.4.1 The ozone layer

The Earth is wrapped in a blanket of air called the 'atmosphere', which is made up of several layers. About 19-30 kilometers above the Earth is a layer of gas called ozone, which is a form of oxygen. Ozone is produced naturally in the atmosphere.

The ozone layer is very important because it stops too many of the sun's 'ultra-violet rays' (UV rays) getting through to the Earth - these are the rays that cause our skin to tan. Too much UV can cause skin cancer and will also harm all plants and animals. Life on Earth could not exist without the protective shield of the ozone layer. The loss of the ozone layer occurs when more ozone is being destroyed than nature is creating.

3.4.2 What causes the ozone hole on human?

One group of gases is particularly likely to damage the ozone layer. These gases are called CFCs, Chloro-Fluoro-Carbons. CFCs are used in some spray cans to force the contents out of the can. They are also used in refrigerators, air conditioning systems and some fire extinguishers. They are used because they are not poisonous and do not catch fire. The ozone layer is like a sunscreen, and a thinning of it would mean that more ultra-violet rays would be reaching us. Too many UV rays would cause more sunburn, and because sunburn causes skin cancer, this too would increase deaths. These UV rays are also dangerous for our eyes and could cause an increase in people becoming blind. That is why sun cream and sunglasses are very important.

Ultraviolet radiation is part of the electromagnetic spectrum (the whole range of radiation that we get from the sun), and is defined as the electromagnetic wavelengths between ~100nm to 400nm. (1nm = nanometer, 10-9m.) This is further subdivided into UV-A (315-400nm), UV-B (280- 315nm), and UV-C (100-280nm). The shorter the wavelength, the more energy it has: UV-C is a very damaging form of UV radiation and most forms of life on Earth would be killed by exposure to it. Fortunately for us no UV-C reaches the Earth's surface because it is all absorbed by ozone (O3) molecules. Most of the UV radiation that does reach the surface is UV-A, because O3 is less efficient at absorbing these longer wavelengths of radiation. A little UV-B also makes it through - UV-B makes up 2-5% of the total UV radiation arriving at the Earth's surface. However, it's the UV-B that does most damage, causing sunburn and skin cancer.

3.4.3 The ozone hole on animals and plants

UV rays can go through water and end up killing small water animals or plants, called 'plankton' which form the base of the food chain in oceans and seas. Whales and other fishes have plankton as their main food, and if plankton dies because of these UV rays, whales will start dying too, because they will not have anything to eat. Large amounts of UV rays could damage all green plants. If the ozone layer keeps getting thinner, there could be fewer and fewer plants on Earth, and then there would be less food in the whole world.

Ozone found between 19 and 30 kilometers high in the atmosphere is one of the reasons why we are alive on Earth. But when the gas ozone is found lower down where we can breathe it in, it becomes very dangerous for our health. This ozone is caused by a reaction between air pollution and sunlight and can cause modern-day smog. This is different to the smog that formed in the early 20th century from smoke and fog.

3.5.1 Consequences of greenhouse affect

Global Warming has a lot of consequences, It can cause the following:

Extreme Weather

Increase Evaporation

Sea Level Rise

Temperature to Rise

Economy such as, Agriculture, Insurance, Transportation

Ecosystems such as, Forests, Mountains, and Ecological productivity

Health by increasing the risk of spreading disease

Sea levels may rise, perhaps by as much as 20 to 40 cm Higher sea levels will threaten the low-lying coastal areas of the world, such as the Netherlands and Bangladesh.

Increase in rainfall.

Disruption of whole ecosystem.

Soil will become infertile.

Plants will be less in N2 susceptible to pests.

Too much UV can cause skin cancer and will also harm all plants and animals.

UV rays can go through water and end up killing small water animals or plants, called 'plankton‘

Large amounts of UV rays could damage all green plants.

A number of diseases, including Lyme disease, hantavirus infections, dengue fever, bubonic plague, and cholera, have been linked to climate change.

As climate change begins to affect our planet to a greater extent the infectious disease carrying organisms will be able to reach higher altitudes and will have a longer season of breeding, increasing the likelihood of a human being in contact with the disease

Malaria can affect 45% of the world’s population today but if global warming continues at the rate that it is progressing, that number could change to be 60% of the world’s population

3.5.2 What else is affected by global warming?

Coral reefs- as the sea level rises the more and more coral reefs are being killed as they are subjected to cooler, darker waters.

Greenland- The country of Greenland, a good percentage of which is made up of ice, is likely to melt significantly should global warming continue, causing sea levels to rise significantly and drowning many coastal communities.

The polar ice caps- as global warming continues the polar ice caps are melting with speed and are diminishing all over the globe, causing many animals who inhabit the same areas as these polar ice caps to lose part of their habitats.

Weather patterns will greatly be affected by global warming as the weather must take into account a warmer climate.

Wetlands- as sea levels rise due to global warming the number of wetlands diminishes as they are drowned by the rising waters.

4.1 Microbial contributions to greenhouse gas emissions

Soil microorganisms are a major component of biogeochemical nutrient cycling and global fluxes of CO2, CH4, and N2. Global soils are estimated to contain twice as much carbon as the atmosphere, making them one of the largest sinks for atmospheric CO2 and organic carbon (Jenkinson and Wild, 1991; Willey et al., 2009). Agriculture releases to the atmosphere significant amounts of CO2, CH4 and N2O (Paustian et al., 2004). Carbon dioxide is released largely from microbial decay or burning of plant litter and soil organic matter (Janzen 2004; Smith 2004b).

Much of this carbon is stored in wetlands, peatlands, and permafrost, where microbial decomposition of carbon is limited. The amount of carbon stored in the soil is dependent on the balance between carbon inputs from leaf litter and root detritus and carbon outputs from microbial respiration underground (Davidson and Janssens, 2006).Soil respiration refers to the overall process by which bacteria and fungi in the soil decompose carbon fixed by plants and other photosynthetic organisms and release it into the atmosphere in the form of CO2. This process accounts for 25% of naturally emitted CO2, which is the most abundant greenhouse gas in the atmosphere and the target of many climate change mitigation efforts. Small changes in decomposition rates could not only affect CO2 emissions in the atmosphere, but may also result in greater changes to the amount of carbon stored in the soil over decades (Davidson and Janssens, 2006).

Atmospheric CO2 levels are increasing at a rate of 0.4% per year and are predicted to double by 2100 largely as a result of human activities such as fossil fuel combustion and land-use changes (Lal, 2005; IPCC, 2007). They found that high CO2 concentrations accelerated average growth rate of plants, thereby allowing them to sequester more CO2. However, this growth was coupled with an increase in soil respiration due to the increase in nutrients available for decomposition by releasing more CO2 into the atmosphere (Willey et al., 2009).Methane is another important greenhouse gas and is 25 times more effective than CO2 at trapping heat radiated from the Earth (Schlesinger and Andrews, 2000).

Microbial methanogenesis is responsible for both natural and human-induced CH4 emissions since methanogenic archaea reduce carbon into methane in anaerobic, carbon-rich environments such as ruminant livestock, rice paddies, landfills, and wetlands. Not all of the methane produced ends up in the atmosphere however, due to methanotrophic bacteria, which oxidize methane into CO2 in the presence of oxygen. When methanogens in the soil produce methane faster than can be used by methanotrophs in higher up oxic soil layers, methane escapes into the atmosphere (Willey et al., 2009).Methane is produced when organic materials decompose in oxygen-deprived conditions, notably from fermentative digestion by ruminant livestock, stored manures and rice grown under flooded conditions (Mosier et al. 1998).

Methane is mainly produced by livestock. This includes enteric fermentation in livestock and manure management. Cow gut is full of bacteria that produce methane (enteric fermentation). Farmers use liquid manure management systems to collect and store manures. The mixture of manure and water, while in storage, generates methane.The growing of rice in flooded fields releases methane from waterlogged soils. Methanotrophs are therefore important regulators of methane fluxes in the atmosphere, but their slow growth rate and firm attachment to soil particles makes them difficult to isolate. Further exploration of these methanotrophs’ nature could potentially help reduce methane emissions if they can be added to the topsoil of landfills, for example, and capture some of the methane that would normally be released into the atmosphere.

Not unlike their role in the carbon cycle, soil microorganisms mediate the nitrogen cycle, making nitrogen available for living organisms before returning it back to the atmosphere.

Nitrous oxide(N2O) is generated by the microbial transformation of nitrogen in soils and manures, and is often enhanced where available nitrogen exceeds plant requirements, especially under wet conditions (Smith & Conen 2004; Oenema et al. 2005).In the process of nitrification (during which ammonia is oxidized to nitrate), microbes release NO and N2O, two critical greenhouse gases, into the atmosphere as intermediates. Evidence suggests that humans are stimulating the production of these greenhouse gases from the application of nitrogen-containing fertilizers (Willey et al., 2009).

When nitrogen is applied to the field as fertilizer, a certain portion of it escapes through evaporation as nitrous oxide. For example, Nitrosomonas eutropha is a nitrifying proteobacteria found in strongly eutrophic environments due to its high tolerance for elevated ammonia concentrations. Nitrogen-fertilizers increase ammonia concentrations, causing N. eutropha to release more NO and N2O in the process of oxidizing ammonium ions. Since NO is necessary for this reaction to occur, its increased emissions cause the cycle to repeat, thereby further contributing to NO and N2O concentrations in the atmosphere (Willey et al., 2009).

Farming is also a source of anthropogenic nitrous oxide (N2O).  N2O is produced during the decay of animal manure in paddocks and from the use of nitrate-based fertilizers (Monteny et al., 2006). Use of slow-release urea-based fertilizers, and of nitrification inhibitors, may reduce agricultural N2O production.

4.2 Microbial response to increased temperatures:

One of the major uncertainties in climate change predictions is the response of soil respiration to increased atmospheric temperatures (Briones et al., 2004; Luo et al., 2001). Several studies show that increased temperatures accelerate rates of microbial decomposition, thereby increasing CO2 emitted by soil respiration and producing a positive feedback to global warming (Allison et al., 2010). Soil microorganisms may also acclimate to higher soil temperatures by adapting their metabolism and eventually return to normal decomposition rates. Lastly, it can be interpreted as an above ground effect if changes in growing-season lengths as a result of climate change affect primary productivity, and thus carbon inputs to the soil (Davidson and Janssens, 2006).

The affects of increased global temperatures on soils is especially alarming when considering the effects it has already begun to have on one of the most important terrestrial carbon sinks: permafrost. Permafrost is permanently frozen soil that stores significant amounts of carbon and organic matter in its frozen layers. As permafrost thaws, the stored carbon and organic nutrients become available for microbial decomposition, which in turn releases CO2 into the atmosphere and causes a positive feedback to warming (Davidson and Janssens, 2006). One estimate suggests that 25% of permafrost could thaw by 2100 as a result of global warming, making about 100 Pg of carbon available for microbial decomposition (Davidson and Janssens, 2006). This could have significant effects on the global carbon flux and may accelerate the predicted impacts of climate change. Moreover, the flooding of thawed permafrost areas creates anaerobic conditions favorable for decomposition by methanogenesis. Although anaerobic processes are likely to proceed more slowly, the release of CH4 into the atmosphere may result in an even stronger positive feedback to climate change (Davidson and Janssens, 2006).

5.1 Mitigation of greenhouse gas- carbon dioxide (CO2) and biomass production

Global warming's affects can be seen worldwide, and many experts believe it's only going to get worse as CO2 emissions continue to rise. Global warming is caused by the emission of greenhouse gases. 72% of the totally emitted greenhouse gases are carbon dioxide (CO2), 18% Methane and 9% Nitrous oxide (N2O). Carbon dioxide emissions therefore are the most important cause of global warming. CO2 is inevitably created by burning fuels like e.g. oil, natural gas, diesel, organic-diesel, petrol, organic-petrol and ethanol. That's the bad news. The good news is that researchers have found that an alga is not only a great source of alternative of natural bio energy but it also has the ability to capture CO2.Microalgae are generally recognized as the most promising solution for both bio-fuel production and industrial capture of emitted CO2. The ability of these photosynthetic microorganisms to convert carbon dioxide into carbon-rich lipids (only a step or two away from bio-diesel) greatly exceeds that of agricultural oleaginous crops, without competing for arable land. The potential of microalgae has been investigated by various EU programmes dedicated to reducing CO2 and other greenhouse gas emissions.

On the other hand, current realizations are very limited and could not lead to break-through in the field. Commercial alga technologies use plantonic algae (Chlamydomonas, Chlorella, Euglena etc.) in water solution in Vertical Bioreactors (VB) or algae farms with large ponds.

There are several disadvantages of these processes: lots of water is needed for the production, CO2 is bubbling through the liquid phase (large pressure drop, low efficiency), preparation of algae is not solved, harvesting is difficult, time consuming and inefficient, difficult scale-up, large foot print.

Opposed to the current methods, the proposed process is based on biofilm technology using Rotating Disk reactor system similar to the state of art rotating reactors used in biological industry elsewhere. In this system algae can be grown on indifferent biocompatible surface and thus CO2 would be captured either from the gas phase directly or from the liquid phase after bubbling. This method would dramatically increase the efficiency and decrease the amount of water necessary for the process. Automatic and continuous harvesting could be designed. Scale up is easy and the foot print would be much smaller than used currently.

When biodiesel is burned it releases carbon dioxide (CO2), which is a major contributor to climate change. However, biodiesel is made from crops that absorb carbon dioxide and give off oxygen. This cycle would maintain the balance of CO2 in the atmosphere, but because of the CO2 emissions from farm equipment and production of fertilizer and pesticides, biodiesel adds more CO2 to the atmosphere than it removes.

5.2 Mitigation of greenhouse gas- Methane (CH4)

Methane is a greenhouse gas that contributes to global warming and climate change. Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities. In 2010, CH4 accounted for about 10% of all U.S. greenhouse gas emissions from human activities. Methane is also emitted from a number of natural sources. Wetlands are the largest source, emitting CH4 from bacteria that decompose organic materials in the absence of oxygen. Smaller sources include termites, oceans, sediments, volcanoes, and wildfires. Methane's lifetime in the atmosphere is much shorter than carbon dioxide (CO2), but CH4 is more efficient at trapping radiation than CO2. Pound for pound, the comparative impact of CH4 on climate change is over 20 times greater than CO2 over a 100-year period. Globally, over 60% of total CH4 emissions come from human activities according to EPA (2010). Methane is emitted from industry, agriculture, and waste management activities, described below.

Industry: Natural gas and petroleum systems are the largest source of CH4 emissions from industry in the United States. Methane is the primary component of natural gas. Some CH4 is emitted to the atmosphere during the production, processing, storage, transmission, and distribution of natural gas. Because gas is often found alongside petroleum, the production, refinement, transportation, and storage of crude oil is also a source of CH4 emissions.

Agriculture: Domestic livestock such as cattle, buffalo, sheep, goats, and camels produce large amounts of CH4 as part of their normal digestive process. Also, when animals' manure is stored or managed in lagoons or holding tanks, CH4 is produced. Because humans raise these animals for food, the emissions are considered human-related. Globally, the Agriculture sector is the primary source of CH4 emissions.

Waste from Homes and Businesses: Methane is generated in landfills as waste decomposes and in the treatment of wastewater. Landfills are the third largest source of CH4 emissions in the United States.

New recovery technologies enable the capture and use of biogas as a fuel source--reducing greenhouse gas emissions.

Methane as Biogas

When animal manure is placed in an oxygen-deprived environment, such as an anaerobic reactor, bacteria decompose the organic material to produce methane. Untreated biogas rises to the top of the anaerobic reactor where it is captured. Untreated biogas can be used in place of fossil fuels to run the reactor, which requires heat, and used in other farm operations. Some of the biogas is flared to control odor but the remaining gas can be used to run natural gas turbines to generate electricity. Other organic material, like food or cheese whey from dairy processing plants, can be added to the reactor to reduce waste volumes and increase methane output.

Agricultural methane recovery is considered a renewable resource and is particularly important to rural areas in meeting increased voltage demand because it originates there; the electric grid is unnecessary to transfer the energy from the source. Biogas facilities also qualify as carbon offset projects; owners can sell carbon credits.

Landfills also produce methane. About 23 percent of all methane emissions come from solid waste landfills. Similar to biogas facilities, waste decomposition within the landfill produces about 50 percent methane and 50 percent carbon dioxide. The methane is extracted from landfills via wells, blower and flares, and vacuum systems. The methane flows to a central point for processing and treatment.

Landfills can transfer natural gas directly to power plants that burn methane to generate electricity. Recovered methane can also be transported to industrial and manufacturing facilities, reducing fossil fuel use. The Environmental Protection Agency estimates that there are approximately six thousand landfills in the United States. Most of these landfills are composed of municipal waste, and, therefore, producing methane. These landfills are the largest source of anthropogenic methane emissions in the United States. Waste Management uses landfill gas as an energy source. Their landfill gas-to-energy projects create enough energy to power four hundred thousand homes every day. This energy production offsets almost two million tons of coal per year. These projects also reduce greenhouse gas emissions into the atmosphere.

Waste Management currently has 110 landfill gas-to-energy facilities. This is a good substitute of natural gas and run the vehicles more efficiently. [1]The gases produced within the landfill can be collected and flared off or used to produce heat or electricity.

[1]"Landfill Gas to Energy". Waste Management. Retrieved 2010-04-26-2010.

Coal bed methane, oil and natural gas operations all produce methane gas. These industries have implemented technologies to recover methane during exploration, transport and delivery processes via specialized well heads and valve designs. Recovered methane is often used to run operations on-site, reducing greenhouse gas emissions.

Recovered methane can be converted to compressed natural gas and liquefied natural gas for vehicle fuel. Natural gas produces less carbon dioxide emissions. Vehicles are large contributors to greenhouse gas emissions, but it is difficult to develop natural gas fueling stations. Government vehicle fleets are an excellent choice for natural gas because central fueling depots are easy infrastructure developments for municipal agencies.

Methane recovery replaces fossil fuel use under certain circumstances, in rural areas, near municipal landfills and government truck fleets. Methane recovery makes it possible to reduce greenhouse gas emissions and solve some energy problems in rural and municipal areas.

Table 1: Reducing Methane Emissions

Emissions Source

How Emissions Can be Reduced

Industry

Upgrading the equipment used to produce, store, and transport oil and gas can reduce many of the leaks that contribute to CH4 emissions. Methane from coal mines can also be captured and used for energy.

Agriculture

Methane can be reduced and captured by altering manure management strategies at livestock operations or animal feeding practices.

Waste from Homes and Businesses

Because CH4 emissions from landfill gas are a major source of CH4 emissions in the United States, emission controls that capture landfill CH4 are an effective reduction strategy.

5.3 Mitigation of greenhouse gas-Nitrous oxide (N2O)

N2O is a greenhouse gas with tremendous global warming potential (GWP). When compared to carbon dioxide (CO2), N2O has 310 times the ability per molecule of gas to trap heat in the atmosphere. N2O is produced naturally in the soil during the microbial processes of nitrification and denitrification. For example, practices that deliver added N more efficiently to crops often suppress the emission of N2O (Bouwman 2001) and managing livestock to make most efficient use of feeds often suppresses the amount of CH4 produced (Clemens & Ahlgrimm 2001). The approaches that best reduce emissions depend on local conditions and therefore vary from region to region.

In 2008, agriculture contributed 6.1% of the total U.S. greenhouse gas emissions and cropland contributed nearly 69% of total direct nitrous oxide (N2O) emissions. Additionally, estimated emissions from agricultural soils were 6% higher in 2008 than 1990.

Scientists have long known about naturally occurring microorganisms called denitrifiers, which fight nitrous oxide by transforming it into harmless nitrogen gas. Loeffler and his team have now discovered that this ability also exists in many other groups of microorganisms, all of which consume nitrous oxide and potentially mitigate emissions. The research team screened available microbial genomes encoding the enzyme systems that catalyze the reduction of the nitrous oxide to harmless nitrogen gas. Microbes with this capability can be found in most, if not all, soils and sediments, indicating that a much larger microbial army contributes to nitrous oxide consumption. "Before we did this study, there was an inconsistency in nitrous oxide emission predictions based on the known processes contributing to nitrous oxide consumption, suggesting the existence of an unaccounted nitrous oxide sink," said Loeffler. "

According to 2006 data from the United States Environmental Protection Agency, industrial sources make up only about 20% of all anthropogenic sources, and include the production of nylon, and the burning of fossil fuel in internal combustion engines. Human activity is thought to account for 30%; tropical soils and oceanic release account for 70% (US EPA, 2006). However, a 2008 study by Nobel Laureate Paul Crutzen suggests that the amount of nitrous oxide release attributable to agricultural nitrate fertilizers has been seriously underestimated, most of which would presumably come under soil and oceanic release in the Environmental Protection Agency data. Atmospheric levels have risen by more than 15% since 1750. Nitrous oxide also causes ozone depletion. A new study suggests that N2O emission currently is the single most important ozone-depleting substance (ODS) emission and is expected to remain the largest throughout the 21st century. (Ravishankara et al., 2009).

The average concentration of nitrous oxide in the atmosphere is now increasing at a rate of 0.2 to 0.3% per year. The role of nitrous oxide in the enhancement of the greenhouse effect is smaller than the other greenhouse gases already discussed, but still represents about 6% of climate forcing though human-induced greenhouse gas emissions. Sources for the increase of nitrous oxide in the atmosphere include land-use conversion, fossil fuel combustion, biomass burning, and soil fertilization. Most of the nitrous oxide added to the atmosphere each year due to human activities comes from agricultural soils, where nitrogen-rich fertilizer and manure is converted to nitrous oxide by soil bacteria. Nitrous oxide is also released into the atmosphere when fossil fuels and biomass are burned.

Aerobic autotrophic nitrification, the stepwise oxidation of ammonia (NH3) to nitrite (NO2−) and to nitrate (NO3−).

Anaerobic heterotrophic denitrification, the stepwise reduction of NO3− to NO2−, nitric oxide (NO), N2O and ultimately N2, where facultative anaerobe bacteria use NO3− as an electron acceptor in the respiration of organic material in the condition of insufficient oxygen (O2) Nitrifier denitrification, which is carried out by autotrophic NH3−oxidizing bacteria and the pathway whereby ammonia (NH3) is oxidized to nitrite (NO2−), followed by the reduction of NO2− to nitric oxide (NO), N2O and molecular nitrogen (N2).

5.4 Mitigation of greenhouse gas- Fluorinated gases (F-gases)

'F-gases' are man-made gases that included chlorofluoracarbons (CFCs), hydrofluorocarbons (HFCs) and sulphur hexafluoride (SF6). They are used as refrigerants, propellants and in electronics manufacture, but are highly persistent in the Earth's atmosphere. They are typically thousands of times more potent as greenhouse gases than carbon dioxide. While reductions in the use of CFCs have been underway in Western Nations for over twenty years, these chemicals are still used in some developing countries. The Montreal Protocol, the international agreement that phases out ozone-depleting substances, requires the end of chlorodifluoromethane production by 2020 in developed countries and 2030 in developing countries. CFCs have been gradually phased out in most nations and replaced by hydrofluorocarbons (HFCs) which avoid ozone depletion problems, but are still very potent greenhouse gases. The Kyoto Protocol aims to reduce emissions of these HFCs by tighter controls and the use of new alternatives such as using butane or propane as the coolant in refrigerators rather than HFCs.

5.5 Mitigation of greenhouse gases through Livestock management

Livestock, predominantly ruminants such as cattle and sheep, are important sources of CH4; accounting for approximately 18% of global anthropogenic emissions of this gas (US-EPA 2006). The methane is produced primarily by enteric fermentation and voided by eructation (Crutzen 1995). Practices for reducing CH4 emissions from this source fall into three general categories: improved feeding practices, use of specific agents or dietary additives, and longer term management changes and animal breeding.

(i) Improved feeding practices

Methane emissions can be reduced by feeding more concentrates, normally replacing forages (Lovett et al., 2003; Beauchemin & McGinn 2005). Although concentrates may increase daily methane emissions, emissions per kilogram feed intake and per kilogram product are almost invariably reduced. The net benefit, however, depends on reduced animal numbers or younger age at slaughter for beef animals and on how the practice affects emissions when producing and transporting the concentrates (Phetteplace et al., 2001; Lovett et al., 2006).

Other practices that can reduce CH4 emissions include: adding oils to the diet (Jordan et al. 2004); improving pasture quality, especially in less developed regions, because it improves animal productivity and reduces the proportion of energy lost as CH4 (Alcock & Hegarty 2005)and optimizing protein intake to reduce N excretion and N2O emissions (Clark et al., 2005).

(ii) Specific agents and dietary additives

A wide range of specific agents, mostly aimed at suppressing methanogenesis, have been proposed as dietary additives to reduce CH4 emissions as follows:

Ionophores are antibiotics that can reduce methane emissions (Van Nevel & Demeyer 1995; McGinn et al., 2004), but their effect may be transitory and they have been banned in the EU.

Halogenated compounds inhibit methanogenic bacteria (Van Nevel & Demeyer 1995) but their effects, too, are often transitory and they can have side effects such as reduced intake.

Probiotics and live micro-organisms, yeast cultures based on Saccharomyces cerevisiae are widely used in ruminant diets. The feeding of such probiotic products is widely associated with increases in livestock production, enhanced ruminal capture of ammonia into microbial protein, improving dietary N usage and reducing emissions. The use of yeast and other live microorganisms to specifically decrease methane emissions has been suggested (Newbold and Rode, 2006); however, to date, the overall effects appear to be rather small and inconsistent (Beauchemin et al., 2008). More experimental approaches based on the addition of acetogens, methane oxidizing organisms (McAllister and Newbold, 2008) have been postulated but, while potentially promising, are some years away from commercial exploitation.

Propionate precursors such as fumarate or malate reduce methane formation by acting as alternative hydrogen acceptors (Newbold et al., 2002), but they elicit response only at high doses and are therefore expensive (Newbold et al., 2005).

Vaccines against methanogenic bacteria are being developed but are not yet commercially available (Wright et al., 2004).

Bovine somatotrophin (bST) and hormonal growth implants do not specifically suppress CH4 formation, but by improving animal performance (Bauman 1992; Schmidely 1993), they can reduce emissions per kilogram of animal product. (McCrabb 2001).

(iii) Longer term management changes and animal breeding

Increasing productivity through breeding and better management practices spreads the energy cost of maintenance across a greater feed intake, often reducing methane output per kilogram of animal product (Boadi et al., 2004). With improved efficiency, meat-producing animals reach slaughter weight at a younger age, with reduced lifetime emissions (Lovett & O'Mara 2002). The whole system effects of such practices are not entirely clear, however; for example, selecting for higher yield might reduce fertility, requiring more replacement animals (Lovett et al., 2006).

5.6 Mitigation of greenhouse gases through manure management

Animal manures can release significant amounts of N2O and CH4 during storage, but the magnitude of these emissions varies. Methane emissions from manure stored in lagoons or tanks can be reduced by cooling or covering the sources, or by capturing the CH4 emitted (Monteny et al., 2001, 2006; Paustian et al., 2004). The manures can also be digested anaerobically to maximize retrieval of CH4 as an energy source (Clemens & Ahlgrimm 2001; Clemens et al.,2006). Storing and handling the manures in solid rather than liquid form can suppress CH4 emissions, but may increase N2O formation (Paustian et al., 2004). Preliminary evidence suggests that covering manure heaps can reduce N2O emissions (Chadwick 2005). For most animals worldwide, there is limited opportunity for manure management, treatment or storage—excretion happens in the field and handling for fuel or fertility amendment occurs when it is dry and methane emissions are negligible (Gonzalez-Avalos & Ruiz-Suarez 2001). To some extent, emissions from manure might be curtailed by altering feeding practices or by composting the manure (Pattey et al., 2005), but these mechanisms and the system-wide influence have not been widely explored. Manures also release GHGs, notably N2O, after application to cropland or deposition on grazing lands, but the practices for reducing these emissions are considered above. There are technologies available that use methane as an energy source. Methane is recovered from manure using anaerobic digesters, which is used to fuel engine generators to generate electricity or boilers to produce hot water.

6. Controlling steps

One ways to mitigate greenhouse gases from the atmosphere such as by planting trees or using algae to absorb carbon dioxide.

Phytoplankton also critical component for depositing biomass/carbonate skeletons when carried into the deep ocean layer and ocean sediment. Accounts for 50 % of net biomass carbon fixation.

Reduction of the consumption of fossil fuels

Greenhouse gas emissions are the byproducts of all our energy-consuming activities.

One good way to prevent global warming is choosing to use power produced by alternative means rather than by the burning of fossil fuels, which give off large amounts of carbon dioxide. Solar energy and wind energy can be a good alternative to use.

Another way we can stop global warming is by attempting to take greenhouse gases out of the atmosphere such as carbon dioxide, the main greenhouse gas, through techniques such as carbon sequestration.

There are four main ideas for carbon sequestration; to store carbon dioxide in the ground, to store carbon dioxide in the ocean floor, to increase the abilities of certain plants and animals to take in carbon dioxide from the atmosphere, and to look at the genome sequences of certain plants and animals who produce methane, hydrogen, or help to store carbon dioxide.

Eco friendly alternative CFC.

Sulphate aerosols

Probiotics and live micro-organisms, yeast cultures based on Saccharomyces cerevisiae are widely used in ruminant diets.

Prevent global warming by reducing your waste electricity use.

Prevent global warming with more efficient light bulbs!

Prevent global warming by turning down your hot water heater.

By making a few simple changes, like driving less when possible and using more energy-efficient appliances, everyone can help to reduce their greenhouse gas emissions.

Leave your car behind. According to the EPA, not driving for just two days each week can lower fossil fuel emissions by an average of 1,600 pounds per year. Find a co-worker with whom you can carpool. Hop on public transportation. Walk or ride a bike to anything within three miles of your home.

Cut down on water consumption in your bathroom. Reducing your consumption of water cuts down on greenhouse gas emissions since it takes a lot of energy from local systems to purify and deliver sanitary water to each household. Turn off the sink while shaving or brushing your teeth.

Do not leave your cell phone charger plugged into the wall if it's not connected to your phone. When anything is plugged in, its draining electricity and contributing to the continued burning of fossil fuels. This applies to anything that could be unplugged when it's not in use: toasters, coffee makers, grills, toaster ovens, fans, TVs.

Replace a few light bulbs in your house with bulbs that have the Energy Star rating. According to the EPA, the new bulbs save 75 percent more energy and last nearly 10 times longer. The added bonus to the consumer is that monthly bills decrease and less money/time is spent on replacing older bulbs in fixtures.

7. Conclusion

Greenhouse gases (GHG) are those gases (e.g.CO2, CH4) present in the atmosphere which reduce the loss of heat into space and therefore contribute to increase global temperature which is detrimental to animal, plant and microorganism, create ozone hole in ozone layer. An increase in the concentration of greenhouse gases leads to an increase in the magnitude of the greenhouse effect. (Called enhanced greenhouse affect) Global warming potential (GWP) is a measure of how much a given mass of greenhouse gas is estimated to contribute to global warming. It is a relative scale which compares the gas in question to that of the same mass of carbon dioxide. CH4 is a potent greenhouse gas with a global warming potential (GWP) ∼23-25 times higher than that of carbon dioxide (CO2).Nitrous oxide with a GWP ∼296-300 times higher than that of carbon dioxide. A single molecule of methane traps about 20 times more heat than one of CO2.

Efforts to reduce the atmospheric concentration of greenhouse gases are termed ‘mitigation’.

Microbiological mitigation is an effective solution to reduce the greenhouse gases (GHG).This necessitates an international effort to strengthen and expand ongoing research and to direct new resources for basic research programs. The magnitude of potential problems associated with global changes demands a broad and aggressive, multidisciplinary scientific response, which must include extensive microbiological research and greater participation by microbial ecologists in the development of the basic knowledge that is essential for informed policy development, regulation and decision-making related to human-environment interactions. Improving carbon management (e.g., reducing net anthropogenic CO 2 emission to the atmosphere by increasing carbon storage in the biosphere).Improving understanding of the budgets and controls of trace gases active in climate and atmospheric chemistry (e.g., Carbon dioxide, Methane, Nitrous oxide) and options for minimizing anthropogenic disturbances of these gases.

Implement policies that promote effective long-term research on the microbiology of global change by: Establishing research programs that are: Multidisciplinary, drawing on microbiology as a whole and on partner disciplines (e.g., soil science, climatology, geology, geochemistry, ecology, oceanography and molecular biology).

Mechanistic in their approach, seeking understanding at a basic level that will provide knowledge necessary for predicting responses of microbes to a globally changing environment

Sustained in duration (more than three to five years) to realize the benefits of multidisciplinary approaches establish programs to train people to solve tomorrow’s complex environmental problems by directing additional resources to undergraduate and graduate multidisciplinary training in microbial ecology, atmospheric chemistry, biogeochemistry, and ecosystem science.

The algae, cyanobacteria are the predominant photosynthetic eukaryotic produces in many aquatic environments. They use atmospheric carbon dioxide (CO2) as a source of carbon for growth and convert it into algal cellular organic material- similar to plants. They are a major component of marine plankton and are the basis of the food chain in the oceans. Nitrobacter sp. is reducing atmospheric N2O; Methane reducing bacteria reduce atmospheric CH4.

We should conscious about our environment; try to save waste of food, feed, electric energy which reduce the amount of production of those things. We should increase the use of green energy (e.g. Biodiesel, bioethanol, microbial fuel cell etc.); biofertilizer, bioplastic etc.