Why Are Atmospheric Levels of Greenhouse Gas Emissions Increasing?
Levels of several important greenhouse gases have increased by about 25 percent since large-scale industrialization began around 150 years ago (Figure 1). During the past 20 years, about three-quarters of human-made carbon dioxide emissions were from burning fossil fuels. Figure 1. Trends in Atmospheric Concentrations and Anthropogenic Emissions of Carbon Dioxide Concentrations of carbon dioxide in the atmosphere are naturally regulated by numerous processes collectively known as the carbon cycle (Figure 2). The movement (flux) of carbon between the atmosphere and the land and oceans is dominated by natural processes, such as plant photosynthesis. While these natural processes can absorb some of the net 6.1 billion metric tons of anthropogenic carbon dioxide emissions produced each year (measured in carbon equivalent terms), an estimated 3.2 billion metric tons is added to the atmosphere annually. The Earths positive imbalance between emissions and absorption results in the continuing
