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).