Chapter 8, Key Finding 1

Global concentrations of carbon dioxide (CO2) and methane (CH4) have increased almost linearly since the First State of the Carbon Cycle Report (CCSP 2007; see Figure 8.1). Over the period 2004 to 2013, global growth rates estimated from the National Oceanic and Atmospheric Administration’s marine boundary layer network average 2.0 ± 0.1 parts per million (ppm) per year for CO2 and 3.8 ± 0.5 parts per billion (ppb) per year for CH4. Global mean CO2 abundance as of 2013 was 395 ppm (compared to preindustrial levels of about 280 ppm), and CH4 stands at more than 1,810 ppb (compared to preindustrial levels of about 720 ppb) (very high confidence).