The amount of warming the Earth experiences is directly dependent on the amount of greenhouse gases in the atmosphere, particularly carbon dioxide (CO2) – a long-lived gas that remains in the atmosphere for decades, centuries, and millennia. Because it lasts so long, it has a long-term influence on climate.

Today’s Climate

The amount of CO2 emitted into the atmosphere has increased every year since 1990, with the exception of 2009, when yearly emissions decreased by 1.3 percent. This exception was in large measure a result of a contraction in global production, capital investment, and consumption. Yet even though emissions in 2009 were lower than those in 2008, they were still the second highest in human history, just behind 2008’s total of 9.45 billion metric tonnes. As we send more and more CO2 into the atmosphere, the atmospheric concentration of the gas rises. In 1990, the amount of CO2 in the atmosphere was 354 parts per million (ppm). By August 2011, it had reached 390 ppm. Although plants, which use CO2 to live and grow, do not mind this extra CO2 in the atmosphere, all oxygen-breathing organisms, including humans, have a little less to breathe. However, the critical problem with rising CO2 levels in the atmosphere has to do with their influence on climate.