Sources and Trends Importance of Energy Use Greenhouse gases are emitted by human activity. These activities range from burning natural gas to produce electricity to consuming gasoline to power our cars, trucks, and buses. Material activity releases greenhouse gases when we produce or dispose of materials. Figure 1 shows 1995 emissions of greenhouse gases by activity and type of gas.
Energy use is obviously the dominant activity, and carbon dioxide the dominant greenhouse gas.
Total emissions in 1995 were 101 million tons CO 2 -equivalent. The rest of this paper will only deal with energy-related emissions. The building sector includes residential and commercial uses of energy. Emissions from electricity production are assigned to the end-use sector in proportion to their use of electricity. The industrial sector has been relatively constant during the last 35 years, increasing only 51 percent, compared to the building and transportation sector increases of 120 percent and 247 percent, respectively.