finding 2.4 : key-message-2-4

Using bottom-up, inventory-based calculations, the Second State of the Carbon Cycle Report (SOCCR2) estimates that the average annual strength of the land-based carbon sink in North America was 606 Tg C per year (±75%) during the 2004 to 2013 time period, compared with the estimated 505 Tg C per year (±50%) in ca. 2003, as reported in the First State of the Carbon Cycle Report (CCSP 2007). There is apparent consistency in the two estimates, given their ranges of uncertainty, with SOCCR2 calculations including additional information on the continental carbon budget. However, large uncertainties remain in some components (very high confidence).



This finding is from chapter 2 of Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report.

Description of evidence base: Key Finding 4 is supported by observational evidence from forest inventories in the United States (Woodall et al., 2015) and Canada (Stinson et al., 2011), atmospheric inverse modeling ensembles (see Ch. 8: Observations of Atmospheric Carbon Dioxide and Methane), terrestrial biosphere model ensembles (Huntzinger et al., 2012), and synthesis studies (Hayes et al., 2012; King et al., 2012, 2015). The U.S. forest sink is maintained because of the net accretion of forest land use in combination with continued forest growth (i.e., forests remaining forests; Woodall et al., 2015, 2016).

New information and remaining uncertainties: Components of the North American carbon cycle measured as part of formal inventory programs, such as the forest and agricultural sectors, are estimated with a high level of certainty. However, other components potentially contribute significantly to the magnitude of the continental carbon sink (see Table 2.2). The largest of these comprises the net emissions from inland waters, which at the continental scale are poorly constrained (i.e., uncertainty is effectively 100% of the estimate). Also contributing substantially to the overall uncertainty are other important components of the land base in regions where measurement gaps exist over large areas, such as in Mexico and the remote northern areas of Canada and Alaska.

Assessment of confidence based on evidence: There is very high confidence that the North American land base has maintained an overall carbon sink over the past decade, with net carbon uptake and storage in the vegetation and soils of natural and managed ecosystems.

Provenance
This finding was derived from figure P.2: P.2. Likelihood and Confidence Evaluation

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