Relation of atmospheric CO2 to tropical sea and air temperatures and precipitation

Associations between the season-to-season changes in CO₂ concentration and the sea-surface temperature in the eastern equatorial Pacific, the tropospheric air temperature, and the precipitation in the tropics are explored. The CO₂ records at Mauna Loa and the South Pole from the Scripps Institution of Oceanography and the GMCC/NOAA program, as well as the GMCC records at Barrow, Alaska and American Samoa were used after the annual cycle and the growth due to fossil fuel emission has been removed. We find that the correlation between CO₂ changes and each of the other variables changes with time. In particular, the period from about 1968 to about 1978 was the period of highest correlation, which was also the period when the climate variables were best correlated with each other. The air temperature and the precipitation were as well correlated with CO₂ changes as was SST. Also, there are individual seasons when the CO₂ changes are much better correlated with the climate variables than at other seasons. Furthermore, El Niño events, while the source of the largest signal in the CO₂ record, are by no means the same from one event to the next. We take these results as further confirmation that the apparent effect of SST on the CO₂ record comes less from changes in the equatorial eastern Pacific Ocean than from climate changes throughout the globe. Climate effects on the terrestrial biosphere seem a likely source of much of the interannual variation in atmospheric CO₂.