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6 The Carbon Market: A Primer for Airports 1.1 Overview of GHGs Key Takeaways for Airports GHGs are compounds that retain heat and at elevated levels have been linked to warming the Earth's temperature. Airport sponsors can control and influence the release of GHGs from a variety of sources and activities undertaken onsite, but the majority of GHG emissions at airports are tenant-controlled. Airport sponsors may be eligible to "earn" offset credits by reducing GHG emissions. GHGs are gases that collect in the atmosphere, absorbing and re-emitting solar radiation through a process commonly referred to as the greenhouse gas effect. With greater concentrations of GHGs in the atmosphere, heat is trapped and contributes to an increase in global temperatures. Some GHGs occur naturally and collect in the atmosphere through natural processes. Other anthropogenic GHGs are created and emitted through human activities. Generally, when people refer to GHGs in the context of the carbon markets, they are referring to the six GHGs emitted through human activity and covered by the Kyoto Protocol. The six Kyoto GHGs include: carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); sulfur hexa- fluoride (SF6); hydrofluorocarbons (HFCs); and perfluorocarbons (PFCs). The Kyoto GHGs have varying levels of contribution to global warming. In order to account for the impacts each GHG has on global warming, a commonly used scale has been developed to measure the global warming potential (GWP) of each GHG. GWP uses a relative scale which measures each GHG to that of the same mass of carbon dioxide. Often GHGs will be expressed in terms of their car- bon dioxide equivalent (CO2e), based on that GHG's GWP (UNFCCC n.d.). For example, 1 tonne of methane emissions, with a GWP of 21, would have a CO2e of 21 tonnes. Equally, 1 tonne of CO2 emissions, with a GWP of 1, would have a CO2e of only 1 tonne. Table 1 presents the global warming potentials of the six Kyoto GHGs. Each of these GHGs is created and emitted in a different manner and through different medi- ums or actions. CO2 enters the atmosphere through the burning of fossil fuels, trees and wood products, solid waste, and as a result of chemical reactions. It is sequestered through part of the Table 1. Greenhouse gas global warming potentials. Greenhouse Gas GWP or CO2e Carbon Dioxide (CO2) 1 Methane (CH4) 21 Nitrous Oxide (N2O) 310 Sulfur hexafluoride (SF6) 23,900 Hydrofluorocarbons (HFCs) Varies by specific HFC (140 11,700) Perfluorocarbons (PFCs) Varies by specific PFC (6,500 9,200) Source: IPCC. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change 2007. Cambridge, United Kingdom: Cambridge University Press, 2007.

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Introduction and Background 7 biological carbon cycle, when it is absorbed by plants. CH4 is generally emitted through the production and transport of coal, oil, and natural gas. Emissions can also be the result of decay or organic waste in landfills or agricultural processes. N2O is produced by both natural and human- related sources. Trace amounts of both CH4 and N2O are released from the combustion of fossil fuels. Soil management, animal manure, sewage treatment, and combustion of some fuels are examples of manmade sources of N2O. HFCs, PFCs, and SF6, known collectively as fluorinated gases, have relatively high GWP and are emitted from a variety of different industrial processes. They are occasionally used as substitutes for ozone-depleting substances (ODS), which the inter- national community has been phasing out for the last few decades. GHG emissions from airports are primarily from combustion sources as presented in Table 2. Note that sources that are directly linked to tenants, i.e. airplane emissions and electricity con- sumed from tenant space, are generally attributed to tenants and not the airport itself. Globally and in the United States, GHG emissions have increased over the past few decades. In the United States alone, GHG emissions increased by 17% between 1990 and 2007 (EPA, Climate Change n.d.). With the large expansion of industrial production to meet the world's growing population, along with increasing quality of life in many developing countries, GHG emissions are expected to continue to rise in the future. With the recent global focus on the impacts and effects of GHGs, many countries have made focused efforts to improve efficiency and promote clean technologies, as well as to educate the public on the impact their daily choices have on the amount of GHGs being emitted. Table 2. Airport GHG emission sources. Source GHG Emission(s) Examples Fossil fuel Primarily CO2 Aircraft--idle, takeoff, in flight, landing, auxiliary combustion power units Trace volumes of CH4 and N2O Vehicles--ground support equipment, maintenance, baggage tractors, shuttle buses, private and public vehicles Stationary equipment--generators, heaters, belt movers Other miscellaneous--construction equipment, flares, fires, etc. Refrigerants HFCs Fugitive refrigeration from vehicles and building HVAC systems Waste CH4 Organic matter decomposition (i.e., food, plant decomposition wastes) Wastewater management Electricity Primarily CO2 Purchased electricity from coal, natural gas and/or consumption petroleum products Trace volumes of CH4 and N2O Onsite electric production from coal, natural gas and/or petroleum products Source: Kim, Brian. Guidebook on Preparing Airport Greenhouse Gas (GHG) Emissions Inventories. Palm Springs, CA: UC Symposium on Aviation Noise and Air Quality, 2009.