The time-mean response over the tropical Pacific region to a quadrupling Of CO2 is investigated using a global coupled ocean-atmosphere general circulation model. Tropical Pacific sea surface temperatures (SSTs) rise by about 4°–5°C. The zonal SST gradient along the equator decreases by about 20%, although it takes about one century (with C02 increasing at 1% per year compounded) for this change to become clearly evident in the model. Over the central equatorial Pacific, the decreased SST gradient is accompanied by similar decreases in the easterly wind stress and westward ocean surface currents and by a local maximum in precipitation increase. Over the entire rising branch region of the Walker circulation, precipitation is enhanced by 15%, but the time-mean upward motion decreases slightly in intensity. The failure of the zonal overturning atmospheric circulation to intensify with a quadrupling of CO2 is surprising in light of the increased time-mean condensation heating over the “warm pool” reg... Abstract The time-mean response over the tropical Pacific region to a quadrupling Of CO2 is investigated using a global coupled ocean-atmosphere general circulation model. Tropical Pacific sea surface temperatures (SSTs) rise by about 4°–5°C. The zonal SST gradient along the equator decreases by about 20%, although it takes about one century (with C02 increasing at 1% per year compounded) for this change to become clearly evident in the model. Over the central equatorial Pacific, the decreased SST gradient is accompanied by similar decreases in the easterly wind stress and westward ocean surface currents and by a local maximum in precipitation increase. Over the entire rising branch region of the Walker circulation, precipitation is enhanced by 15%, but the time-mean upward motion decreases slightly in intensity. The failure of the zonal overturning atmospheric circulation to intensify with a quadrupling of CO2 is surprising in light of the increased time-mean condensation heating over the “warm pool” reg...