Comment on Qian et al. 2008: La Niña and El Niño composites of atmospheric CO₂ change

Abstract

It is well known that interannual extremes in the rate of change of atmospheric CO₂ are strongly influenced by the occurrence of El Niño-Southern Oscillation (ENSO) events. Qian et al. presented ENSO composites of atmospheric CO₂ changes. We show that their composites do not reflect the atmospheric changes that are most relevant to understanding the role of ENSO on atmospheric CO₂ variability. We present here composites of atmospheric CO₂ change that differ markedly from those of Qian et al., and reveal previously unreported asymmetries between the effects on the global carbon system of El Niño and La Niña events. The calendar-year timing differs; La Niña changes in atmospheric CO₂ typically occur primarily over September–May, while El Niño changes occur primarily over December–August. And the net concentration change is quite different; La Niña changes are about half the size of El Niño changes. These results illustrate new aspects of the ENSO/global carbon budget interaction and provide useful global-scale benchmarks for the evaluation of Earth System Model studies of the carbon system.

• carbon dioxide
• El Nino
• La Nina
• atmospheric variability
• emissions
• concentration change

5. Acknowledgments

This work was supported by NOAA Pacific Marine Environmental Laboratory Contribution 3509; by NOAA's Climate Observation Program, NOAA's Pacific Marine Environmental Laboratory; and by the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement No. NA17RJ1232. This is also JISAO Contribution 1799. The authors thank the two anonymous reviewers for their time and helpful comments.