Monsoon ecosystems control on atmospheric CO2interannual variability: Inferred from a significant positive correlation between year-to-year changes in land precipitation and atmospheric CO2growth rate

Abstract

Previously, large interannual variability were observed of atmospheric CO2 mixing ratio at Mauna Loa Observatory, and were found to be positively correlated with the global near-surface air temperature variability, notably over El Nino-Southern Oscillation (ENSO) cycles, and negatively correlated with global precipitation on the decadal time-scale. By contrast, here we report a significant positive correlation between the interannual variability of CO2 growth rate and the year-to-year changes in global land precipitation. The interannual extremes in the rate of CO2 growth coincide with the largest year-to-year changes in precipitation over land, particularly Indian summer monsoon. We suggest that this positive correlation results mainly from changes in terrestrial net ecosystem production (NEP) with incoming solar radiation: an increase of clouds concurrent with precipitation reduces seasonal NEP and causes a positive anomaly in CO2 emission from the terrestrial biosphere.