Projected Carbon Dioxide Levels for the Year 2020 in Phoenix, Arizona

Previous studies have demonstrated profound increases to CO2 levels in the Phoenix, Arizona metropolitan area and this increase is linked to anthropogenic sources, including traffic volume, land-use patterns, and human population. These studies all agree that vehicular emission is the largest CO2 source in urban areas. Our goal, therefore, is to predict CO2 levels in the Phoenix area for the year 2020 under different fuel-efficiency-standards scenarios. In February 2002, legislation was introduced to increase Corporate Average Fuel Economy (CAFE) standards for personal vehicles by 30%. In this study, we present three scenarios for projected CO2 levels for the year 2020 in the Phoenix metropolitan area. In one scenario, we assume that fuel efficiency remains the same, representing no changes to CAFE standards. In the other two scenarios, we reflect possible changes to the standards: one based on the 30% increase in efficiency as proposed and the second based on a 15% increase in efficiency standards. These scenarios were created through a geographic information system model of current and future CO2 emissions. The model was based on data from current CO2 levels from land use, traffic, and population and projected CO2 levels from the same sources. Results show a decrease in CO2 emissions from soils as a result of land-use conversion from agriculture to urban. Additionally, results show an increase in the CO2 levels for the year 2020 compared with 2000 under the 15% increase in CAFE standards and no change in CAFE standards. Under a 30% increase in CAFE standards, CO2 emissions decreased below 2000 levels. The global carbon budget refers to exchanges in atmospheric carbon dioxide (CO2) through global sources and sinks of carbon. Corresponding with combustion associated with the industrial revolution 150 years ago, changes to the global carbon budget have occurred. Many coordinated efforts have been established to understand how human activities affect the global carbon budget by examining the process by which the oceans and terrestrial biosphere store and exchange carbon with the atmosphere (IPCC 2001; Houghton and others 1990; Law and Simmonds 1996; Keeling and others 1996). Without exception, human activities—mostly concentrated in urban areas—have changed the global carbon budget due to greater population, fossil fuel combustion, land-use conversion, and cement plants. There remains general consensus that CO2 levels are higher in urban areas, despite differences in data collection methods, analysis techniques, and local meteorological conditions. Even though direct comparisons are difficult to make, several studies report that urban levels are higher than rural areas: urban areas in Nottingham, England are 5 ppmv higher than the surrounding rural areas (Berry and Colls 1990), 20 ppmv higher in suburban Vancouver, British Columbia (Reid and Steyn 1997), 30 ppmv higher in an urban canyon Fukuoka City, Japan (Takagi and others 1998), 90 ppmv higher in Cincinnati, Ohio, and 185 ppmv higher in Phoenix, Arizona. In Phoenix, the higher CO2 levels have been linked to anthropogenic sources, including traffic volume, land-use patterns, and human population (Idso and others 1998a, 1998b; Koerner and Klopatek 2002; Wentz and others 2002; Day and others 2002). Despite the interest in examining CO2 in an urban setting, models predicting future levels of CO2 have remained largely global in scale. The Intergovernmental Panel on Climate Change (IPCC 2001) reports three different models, each projecting different levels of CO2. The most commonly used model reports a 1% per year compound increase of CO2 with a doubling of CO2 by year 2070. Models report an increase from 540 to 970 ppmv by the year 2100, which is 90–250% higher than it was in the 1700s (IPCC 2001). Current global average of CO2 is 370 ppmv, about 95 ppmv greater