title: Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years.
abstract: One of the greatest sources of uncertainty for future climate predictions is the response of the global carbon cycle to climate change. Although approximately one-half of total CO(2) emissions is at present taken up by combined land and ocean carbon reservoirs, models predict a decline in future carbon uptake by these reservoirs, resulting in a positive carbon-climate feedback. Several recent studies suggest that rates of carbon uptake by the land and ocean have remained constant or declined in recent decades. Other work, however, has called into question the reported decline. Here we use global-scale atmospheric CO(2) measurements, CO(2) emission inventories and their full range of uncertainties to calculate changes in global CO(2) sources and sinks during the past 50 years. Our mass balance analysis shows that net global carbon uptake has increased significantly by about 0.05 billion tonnes of carbon per year and that global carbon uptake doubled, from 2.4 ± 0.8 to 5.0 ± 0.9 billion tonnes per year, between 1960 and 2010. Therefore, it is very unlikely that both land and ocean carbon sinks have decreased on a global scale. Since 1959, approximately 350 billion tonnes of carbon have been emitted by humans to the atmosphere, of which about 55 per cent has moved into the land and oceans. Thus, identifying the mechanisms and locations responsible for increasing global carbon uptake remains a critical challenge in constraining the modern global carbon budget and predicting future carbon-climate interactions.
authors.affiliation: Department of Geology, University of Colorado, Boulder, Colorado 80309, USA. apballantyne@gmail.com
authors.forename: A P
authors.initials: AP
authors.lastname: Ballantyne
authors.forename: C B
authors.initials: CB
authors.lastname: Alden
authors.forename: J B
authors.initials: JB
authors.lastname: Miller
authors.forename: P P
authors.initials: PP
authors.lastname: Tans
authors.forename: J W C
authors.initials: JW
authors.lastname: White
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002244:Carbon / Q000032:analysis; D002245:Carbon Dioxide / Q000032:analysis* / Q000266:history; D057965:Carbon Sequestration; D057231:Climate Change / Q000706:statistics & numerical data*; D049673:History, 20th Century; D049674:History, 21st Century; D006802:Human Activities; D008962:Models, Theoretical; D009792:Oceans and Seas; D012623:Seawater / Q000737:chemistry*; D013997:Time Factors; D035501:Uncertainty
chemical_list: D002245:Carbon Dioxide; D002244:Carbon