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4 Environmental Analysis 4.8 Greenhouse Gas Emissions enables all GHG emissions to be considered as a group despite their varying GWP. The GWP of each GHG is multiplied by the prevalence of that gas to produce CO2e. These GWPs have been adopted by the U.S. Environmental Protection Agency (USEPA) into 40 Code of Federal Regulations (CFR) 98, Mandatory Greenhouse Gas Reporting. Historically, GHG emission inventories have been calculated using the GWPs from the IPCC's Second Assessment Report (SAR). In 2007, the IPCC updated the GWP values based on the latest science at the time in its Fourth Assessment Report (AR4; IPCC 2007). The updated GWPs in the IPCC AR4 are used in recent GHG emissions inventories. In 2013, the IPCC again updated the GWP values based on the latest science in its Fifth Assessment Report (AR5) (IPCC 2013). However, United Nations Framework Convention on Climate Change (UNFCCC) reporting guidelines for national inventories require the use of GWP values from the AR4. To comply with international reporting standards under the UNFCCC, official emission estimates for California and the U.S. are reported using AR4 GWP values, and statewide and national GHG inventories have not yet updated their GWP values to the AR5 values. By applying the GWP ratios, Project- related CO2e emissions can be tabulated in metric tons per year. Typically, the GWP ratio corresponding to the warming potential Of CO2 over a 100-year period is used as a baseline. The atmospheric lifetime and GWP of selected GHGs are summarized in Table 4.8-1. Table 4.8-1. Global Warming Potentials and Atmospheric Lifetimes Atmospheric Lifetime Global Warming LPotential Greenhouse Gas'1,24 (years) (100-year time horizon)Jorizo Carbon Dioxide(CO2) 50 to 200 1 Methane(CH4) 12 25 Nitrous Oxide(N20) 114 298 HFC-324a 14 1,430 PFC:Tetrafluoromethane(CF4) 50,000 7,390 PFC:Hexafluoroethane(C2F6) 10,000 12,200 Sulfur Hexafluoride(SF6) 3,200 22,800 Source: IPCC 2007 HFC-hydrofluorocarbon;PFC-perfluorocarbon 4.8.2 Regulatory Setting 4.8.2.1 Federal The U.S. Supreme Court ruled on April 2, 2007, that CO2 is an air pollutant as defined under the Clean Air Act (CAA), and that the USEPA has the authority to regulate emissions of GHGs. Responding to the mounting issue of climate change, the USEPA has taken actions to regulate, monitor, and potentially reduce GHG emissions. Mandatory Greenhouse Gas Reporting Rule On September 22, 2009, the USEPA issued a final rule for mandatory reporting of GHGs from large GHG emissions sources in the U.S. (40 CFR 98). In general, this national reporting requirement will provide the USEPA with accurate and timely GHG emissions data from facilities that emit 25,000 MT or more of CO2 per year. These publicly available data allow the reporters to track their own emissions, compare them to similar facilities, and help identify cost-effective opportunities to reduce emissions in the future. Reporting is at the facility level, except that certain suppliers of fossil fuels and industrial GHGs along with vehicle and engine manufacturers report Griffith Energy Storage Project 4.8-3 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023