Using Antarctic ice-core records, we determine for each Antarctic Isotope Maximum (AIM) of Marine Isotope Stage 3 (MIS-3: ca. 28,000 to 59,000 years before present) the rates and durations of warming and atmospheric CO₂ rise. We find that the AIM warming rates significantly decrease as the climate cools from early to late MIS-3. In contrast, the rate of CO₂ rise during AIMs shows no significant trend across this interval. We further find that the AIM warming rate is not sensitive to Heinrich (H) events, contrasting with CO₂, which rises for significantly longer time (compared to the temperature rise) during AIMs which coincide with H events. These distinct Antarctic temperature and CO₂ responses to varying background climate and H events challenge the view that millennial-scale CO₂ and Antarctic temperature changes are dominated by the same physical processes, suggesting an important contribution of low-to-mid-latitude processes to the CO₂ rises.