Chapter 3 Greenhouse Gas Contribution on Climate Change
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- 3.2.1 Water Vapor (H 2 O)
- 3.2.2 Carbon Dioxide (CO 2 )
- Figure 3.2.
- Process Number of sources Emissions (MtCO 2 yr -1 )
- Component Content
- 3.3 Current Scenario of Greenhouse Gases
- Greenhouse gas Pre-1750 tropospheric concentration Current tropospheric concentration
- Figure 3.3.
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CHAPTER 3 Greenhouse Gas Contribution on Climate Change Gurpreet S. Dhillon, Ajila C. M, Surinder Kaur, Satinder K. Brar, Mausam Verma, R.D. Tyagi, and Rao Y. Surampalli 3.1 Introduction Earth is made inhabitable by a layer of greenhouse gases (GHGs) present in the atmosphere which reflect sun radiations back to the Earth’s surface. GHGs, such as carbon dioxide, water vapor, methane, nitrous oxide, ozone and fluorocarbons act as natural temperature regulators. In the past century, the GHGs layer has become thicker, and it has resulted in continuous increase in temperature i.e. global warming. Due to human activities in the recent years, the concentration of GHGs is increasing at very fast pace. The increase in concentration of GHGs has an alarming impact on the environment. Global warming results in melting of the glaciers/ice caps and causes rise in sea levels, droughts, hurricanes, floods, forest fires with greater rage, which are threatening fragile eco-systems and affecting migration of species. The increasing anthropogenic concentration of carbon dioxide in the atmosphere has resulted in ocean acidification threatening marine ecosystems (Buseck and Posfai 1999). GHGs act as Earth’s natural shield which helps to maintain the temperature needed for survival of life, i.e., 53oF (15oC), which is 33oC warmer than with an atmosphere without GHGs. The greenhouse effect is defined as the rise in temperature level of the Earth due to the presence of GHGs in the atmosphere, such as water vapor, CO2, N2O, O3, fluorocarbons and CH4 which have the ability to trap solar energy.Climate is primarily influenced by Earth’s energy budget, which depends on radiation received from the sun and energy radiated back to the atmosphere. Incoming solar radiations are basically in the visible range, whereas the exiting radiations are in the infrared (IR) region. GHGs, such as H2O, CO2, CH4, and N2O absorb IR and radiate it back to the Earth’s surface as shown in Figure 3.1. In addition to GHGs, aerosol particles (suspensions of solid or liquid particles in air), such as volcanic mineral emissions, desert dust, re-entrained road dust, sea salt, sulfates, carbonaceous materials, organic compounds, among others, also exert an important influence on global climate. The aerosol particles are ubiquitous in troposphere, and they can locally intensify or moderate the effects of GHGs through the scattering or absorption of both incoming solar radiation and thermal radiation emitted from the Earth’s surface as well as by acting as cloud condensation nuclei (CCN) and modify the radiative properties of clouds. However, the influence of aerosol particles on Earth’s radiation balance is less widely realized; the role of air-borne minerals has be identified only quite recently (Buseck and Posfai 1999). According to the effectiveness of absorbing long wave radiations, the different GHGs are placed in the following order (IPCC 2007a): a) water vapor: 36–70%; b) carbon dioxide: 9–26%; c) methane: 4–9%; and d) ozone: 3–7%. GHGs do not have any effect on the incoming solar radiation (shortwave radiation). The sunlight is absorbed by the Earth’s environment. Heat from the Earth’s surface radiates up to the atmosphere in the infrared energy form (long wave radiation), which is absorbed by the GHGs. Therefore, GHGs act as a shield and protect these long wave radiations to pass through. In the absence of GHGs, heat would escape back into space, and Earth’s average temperature would be about 60ºF (-18oC) colder which will not be suitable for the living beings. From the last few decades, the concentration of these GHGs is rising alarmingly at enormous rates which pose negative effects on climate. The increasing Earth’s temperature leads to the phenomenon known as global warming. Due to global warming, our planet is coping with adverse consequences, such as severe floods and droughts, rising sea levels, high prevalence of insects, changes in Earth`s precipitation. These environmental changes have several catastrophic effects on society, such as health problems and decreasing economic development. In recent years, various organizations have been concerned with rising GHGs concentrations. After the 1997 Kyoto Protocol, different strategies have been devised for reduction of GHGs emissions in the environment. In the given context, this chapter discusses in detail about the GHGs and their impact on climate change, factors responsible for increasing concentrations of GHGs/global warming and various causes of climate changes. This chapter also covers impact of climate change on environment, human health and on Marine Eco-Systems. Finally, the government initiatives on climate change and challenge of limiting global warming to 2 oC are discussed in detail. 3.2 Greenhouse Gases Gases, such as carbon dioxide are known as long-lived gases, remaining semi-permanently in the atmospheres that do not respond chemically or physically to changes in temperature. These gases are described as ‘‘forcing’’ climate whereas other gases, such as water vapour which respond chemically/physically to changes in temperature are termed as ‘‘feedbacks.’’ Therefore, the increasing GHGs concentration in the environment has impact on the climate and thus affects various organisms. Figure 3.2 shows the distribution of GHGs in the Earth’s environment. Different GHGs are described as follows. 3.2.1 Water Vapor (H2O) Water vapour is not considered as the major component to have effect on long-term climate change. It is the most abundant GHGs. It is naturally cycled into and out of the atmosphere on a relatively short time period. As the Earth’s atmosphere warms, water vapour increases but so does the likelihood of clouds and precipitation. The water vapour is considered as the most important ‘‘feedback’’ mechanism to the greenhouse effect. 
Figure 3.1. The energy balance in the atmosphere (modified from http://zebu.uoregon. edu/1998/es202/l13.html.). The digits donate energy absorbed or emitted in % 3.2.2 Carbon Dioxide (CO2) CO2 is one of the most prominent among all GHGs. Burning of fossil fuels, respiration, volcanic eruptions and deforestation are the major causes of rising CO2 concentration in the Earth’s environment. According to World Energy Council, the worldwide carbon dioxide emissions from burning fossil fuels increased by 12% from 1990 to 1995 (Prax, 2011). Due to human activities, 30 billion tons of CO2 is emitted in the atmosphere which is 30% more than in 1750 (Envirolink 1998). The carbon dioxide emissions increased by 2.8% worldwide in 1996. The U.S. was leading with 25% of total emissions and reported an increase of 3.3% in 1996. Developing countries were responsible for 3 times more carbon dioxide emissions than developed countries. During 1990–95, carbon dioxide emissions from burning fossil fuels increased 35%, Africa increased by 12% and Eastern Europe increased by 75%. CO2 is the most important long-lived ‘‘forcing’’ of climate change. The industrial activities of worldwide large stationary CO2 sources with emissions of more than 0.1 MtCO2 per year are given in Table 3.1. 
Figure 3.2. Distribution of GHGs in Earth’s atmosphere (modified from http://www. abcnews.com) Table 3.1. Summary by process or industrial activity of worldwide large stationary CO2 sources with emissions of more than 0.1 MtCO2 per year
Citation source: IPCC (2005) 3.2.3 Methane Methane is 25 times more potent as a GHG than carbon dioxide. Methane is mainly released from landfills resulting from dumping of municipal solid waste (MSW) and other industrial wastes. Each year, approximately hundreds of millions of tons of municipal solid waste (MSW) is produced, e.g., 254 million tons of MSW was generated in 2007 in the U.S. (USEPA 2008), with a similar amount of industrial wastes around the world. Globally, landfills are the 3rd largest anthropogenic (human-induced) emission source accounting for nearly 12% of global methane emissions or about 750 million metric tons of CO2 equivalents (MMTCO2E), (USEPA 2006). Methane makes up about 25% or even more of the anthropogenic contribution to global warming (IPCC 1992). Moreover, methane oxidation (45 g/m2-d) to CO2 has been observed in a soil-covering landfill in the presence of methanogenic bacteria (Whalen et al. 1990). Landfill gas (LFG) also contains volatile organic compounds (VOCs) that can contribute to the formation of photochemical smog. The typical composition of raw landfill gas is given in Table 3.2. Table 3.2. Typical composition of raw landfill gas (composition by volume unless otherwise stated)
Methane emissions from municipal landfills represent 3% of the total US GHG emissions that contribute to climate change. In 1994, the US Environmental Protection Agency (USEPA) created the Landfill Methane Outreach Program (LMOP), with the objective of reducing landfill GHGs emissions by promoting the development of landfill-gas-to-energy projects (Jaramillo and Matthews 2005). Landfill gas (LFG) results from the biological decomposition of organic matter of municipal solid waste and is a flammable and odorous gaseous mixture, consisting mostly of methane (CH4) and carbon dioxide (CO2) together with a few parts per million (ppm) of hydrogen sulphide (H2S), nitrogen (N2) and volatile organic compounds (VOCs) (Qin et al. 2001; Liamsanguan and Gheewala 2008). Harvesting LFG to generate energy not only encourages more efficient collection thereby reducing GHGs emissions into the atmosphere but also generates revenues for economic development. Bacteria inhabiting livestock, such as cows, buffaloes, sheep, goats and camels produce methane naturally. Every year 350–500 million ton of methane is added to the environment mainly by raising livestock, rice fields, landfill gases, coal mining and drilling for oil and natural gases (WBE 1982; USEPA 2006). Methane has a half-life of only 12 years, but it traps 20 times more heat than CO2. The concentration of methane has doubled since 1750 and is expected to be doubled again by 2050 as given in Table 3.2. 3.2.4 Nitrous Oxide Nitrous oxide is a GHG released from oceans and by bacteria in soils. N2O has increased by 15% since 1750, and 7–13 million tons of N2O is added into the atmosphere, mainly by using nitrogen based fertilizers, disposing of human and animal waste and automobiles exhaust, nitric oxide production, biomass burning and various other sources. The half-life of N2O is 114 years, which makes it necessary to cut-off the N2O emissions (Blasing 2009). 3.2.5 Fluorocarbons Fluorocarbons are a group of synthetic organic compounds which contains fluorine and carbon, such as chlorofluorocarbons (CFCs). CFCs possesses an inherent property of phase change, i.e., they can be easily converted from gas to liquid or liquid to gas phase due to which they can be used in aerosol cans, refrigerators and air conditioners. There is well established fact that CFCs, when released into the environment, breakdown molecules in the Earth’s ozone layer (WBE 1982b) and are thus responsible for the widening of the ozone hole in the atmosphere. Due to this reason, the production of CFCs is banned in United States and the use of CFCs has significantly decreased since then. Nevertheless, other countries also have to follow suit and impose such norms. Hydrofluorocarbons (HFCs) have replaced the CFCs. HFCs do not breakdown the ozone molecules but still are laden with some problems which affect the climate. They trap the heat in the atmosphere aiding in global warming. HFCs are used as coolant in the refrigerators and air conditioners. The coolant should be recycled; leaks should be properly sealed; the coolant should be recovered during dumping of the both devices, which is the only way to strategically reduce emission of this GHGs. 3.3 Current Scenario of Greenhouse Gases Effects of GHGs on climate are clearly evident from observation reported by Ruddiman (2001). According to him, within last 100,000 years the concentrations of carbon dioxide have cycled between low (190 ppm) and high (300 ppm) values. The high levels of CO2 occur in warmer periods and low CO2 occurs in cooler periods. Recent GHGs concentrations present in the atmosphere are given in Table 3.3. Table 3.3. Trends in recent GHG concentrations (IPCC 2007a; Blasing 2009)
Abbreviations: ppm = parts per million; ppb = parts per billion; ppt = parts per trillion; and W/m2 = Watts per square meter During the past 20,000 years, Earth’s climate has been dominated by a cyclic development of long glacial periods intermittently followed by short warmer interglacial periods. The climate was also influenced by natural climate fluctuations on shorter time-scales (Bonan 2002). The current interglacial period, which has seen an expansion of human beings and civilization all over the Earth, is named the Holocene (Roberts 1998). At the end of December 2008, researchers measured an additional 16.2 billion tons of CO2 and 12.2 million tons of CH4 in the atmosphere. Total global CO2 concentrations were the highest with 386 ppm, compared to 280 ppm before the industrial revolution began in the 1800s (Science Daily 2009). Radiative forcing is a measure of how the energy balance of the Earth-atmosphere system is influenced when climate affecting factors, such as GHGs are altered. According to IPCC (2007a), the radiative forcing of climate from 1750 to 2005 with the net forcing due to human activities has been found to be positive i.e. with respect to global warming as given in Fig 3.3. 
Figure 3.3. Radiative forcing of climate between 1750 and 2005 (IPCC 2007a) 3.4 Factors Responsible for Increasing Concentrations of Greenhouse Gases/Global Warming Several theories have emerged to explain the phenomenon of global warming. Among all these theories, anthropogenic global warming (AGW) is considered as the foremost theory which holds human beings responsible for most of the slight warming trend seen since the little ice age. According to the scientific report issued by the IPCC (2007a), the burning of fossil fuels and other human endeavour are causing global warming. Till date, human activity has been altered between a third and a half of Earth’s land surface by different activities, especially farming, pasture, forestry and urbanization (Vitousek et al. 1997). These human activities have consequences on key biogeochemistry cycles, changing the composition of atmosphere resulting in considerable alterations of ecosystems (Foley et al. 2005). Land-use changes result in biogeochemical climatic effects through alteration of the vegetation and soil carbon pools (Houghton and Goodale 2004), as well as modification of the hydrological cycle (Gordon et al. 2005). These changes influence atmospheric greenhouse gas levels and the global climate (Foley et al. 2003). Human activities, such as land clearing, industrial emissions and transportation emissions increase GHGs and aerosols. Since pre-industrial times, CO2 growth has increased by more than 2% each year. Ever since 1800, the growth rate of CO2 concentrations has been doubling after every 31 years. At the same pace, the CO2 concentrations will be expected to reach 560 ppm, almost double than the pre-industrial revolution values by the year 2050 (Hofman et al. 2009). The humans are responsible for 2 ppm rise in CO2 per year at a rate that is 2,000 times more than the natural rate over the past thousands of years. This sudden increase in atmospheric CO2 concentrations is the reason behind the climate change since 1970s. The concentration of GHGs from year 0 to 2005 is provided in Fig. 3.4. 
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