The Issue

Climate change is the result of an increase in heat-trapping (greenhouse) gases in the atmosphere. Carbon dioxide (CO₂) is the major long-lived greenhouse gas (GHG). The burning of fossil fuels (to provide electricity, heat and transportation, and to support industry and agriculture), as well as deforestation, leads to net emissions of CO₂ and increased levels of atmospheric CO₂. The atmospheric concentration of CO₂ has increased from a preindustrial level of 270–280 parts per million (ppm) to a level of approximately 392 ppm in 2012 (see Figure 1).

Global temperature records have been reported independently by scientists at the National Aeronautics and Space Administration (NASA) in the U.S., the National Oceanic and Atmospheric Administration in the U.S., the Climate Research Unit at the University of East Anglia in the U.K. and the Japanese Meteorological Agency. The records from these four independent groups are in good agreement and show a distinct warming trend over the past century. The past decade was the warmest decade in the instrumental temperature record. As shown in Figure 2, the warming trend is continuing, and 2011 was among the warmest years on record. Independent measurements of rising sea levels, increasing acidification of the oceans, loss of Arctic sea ice and the retreat of glaciers around the world are consistent with the impact of rising GHG concentrations and global temperature.

Global Emissions

Figure 3 (below) provides a breakdown of estimated 2009 fossil fuel CO₂ emissions by region. For the U.S. and Europe, the emissions are further broken down by sector and by mode in the transportation sector. The data were taken from reports published by the International Energy Agency, the European Environment Agency and the U.S. Environmental Protection Agency. Globally, emissions from cars and light-duty trucks comprise about 11 percent of all fossil fuel CO₂ emissions. In the U.S., cars and light-duty trucks account for approximately 20 percent of fossil fuel CO₂ emissions, or approximately 4 percent of global fossil fuel CO₂ emissions. In Europe, passenger cars and light-duty trucks account for approximately 19 percent of fossil fuel CO₂ emissions, or about 3 percent of global fossil fuel CO₂ emissions.

Until approximately 2007, the U.S. was the largest CO₂ emitter. Due to economic development, however, emissions from China surpassed those from the U.S. approximately 5 years ago, and it is expected that the gap between emissions from China and those from the U.S. will continue to widen in the future. That said, per capita emissions of CO₂ in the U.S. are expected to remain higher (currently by approximately a factor of four) than those in China.