Global Atmospheric Concentrations of Carbon Dioxide Over Time

Greenhouse gases from human activities are the most significant driver of observed climate change since the mid-20 th  century. 1  The indicators in this chapter characterize emissions of the major greenhouse gases resulting from human activities, the concentrations of these gases in the atmosphere, and how emissions and concentrations have changed over time. When comparing emissions of different gases, these indicators use a concept called “global warming potential” to convert amounts of other gases into carbon dioxide equivalents.