Chapter 1, Key Finding 4
Net CO2 uptake by land and ocean removes about half of annually emitted CO2 from the atmo- sphere, helping to keep concentrations much lower than would be expected if all emitted CO2 remained in the atmosphere. The most recent estimates of net removal by the land, which accounts for inland water emissions of about 1 petagram of carbon (Pg C) per year, indicate that an average of 3.0 ± 0.8 Pg C per year were removed from the atmosphere between 2007 and 2016. Removal by the ocean for the same period was 2.4 ± 0.5 Pg C per year. Unlike CO2, CH4 an atmospheric chemical sink that nearly balances total global emissions and gives it an atmospheric lifetime of about 9 to 10 years. The magnitude of future land and ocean carbon sinks is uncertain because the responses of the carbon cycle to future changes in climate are uncertain. The sinks may be increased by mitigation activities such as afforestation or improved cropping practices, or they may be decreased by natural and anthropogenic disturbances (high confidence).