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. ¿ 2000 American Geophysical Union