Abstract
The global uptake of carbon by land plants may be greater than previously thought, according to observations based on the enigmatic Keeling curve of rising atmospheric carbon dioxide. See Letter p.579 Quantifying global-scale carbon assimilation by plants, or gross primary production (GPP), has been difficult because there are no direct measures at scales greater than the leaf level. An analysis of nearly 30 years of unpublished records of the oxygen isotope (18O/16O) composition of atmospheric carbon dioxide from sampling sites worldwide has provided a means of estimating the GPP that is not reliant on modelling. The data reveal previously unrecognized interannual fluctuations that are driven by El Nino climate events. The effect propagates from the tropics to higher latitudes through the tropical hydrological cycle. Recovery from El Nino events is rapid, implying a shorter turnover time for CO2 than is generally assumed, and suggests a best-guess figure for global GPP of 150–175 petagrams of carbon per year, rather than the current estimate of 120 petagrams.
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