Removal of the southern oscillation effect from the CO2 records at Mauna Loa, Hawaii, and the South Pole reveals corresponding decreases following the Agung eruption in 1963. The period of the decreases roughly corresponds to the period of reduced solar transmittance, as measured at Mauna Loa. It is suggested that the decrease in CO2 level is due to reduced sea surface temperatures, for which there is some direct evidence. The temperature anomaly required to produce the CO2 level dip is calculated on the basis of several simple models and found to be close to that observed.