It is often said that in the past, CO2 changes have lagged temperature changes. Should we now rethink this assertion?

Carbon Dioxide Is the Missing Link to Past Global Climate Changes
http://www.sciencedaily.com/releases/2010/06/100617143936.htm

…/releases/2010/06/100617143936.htm

Increasingly, the Earth's climate appears to be more connected than anyone would have imagined. El Nino, the weather pattern that originates in a patch of the equatorial Pacific, can spawn heat waves and droughts as far away as Africa.

Now, a research team led by Brown University has established that the climate in the tropics over at least the last 2.7 million years changed in lockstep with the cyclical spread and retreat of ice sheets thousands of miles away in the Northern Hemisphere. The findings appear to cement the link between the recent Ice Ages and temperature changes in tropical oceans. Based on that new link, the scientists conclude that carbon dioxide has played the lead role in dictating global climate patterns, beginning with the Ice Ages and continuing today.

Science 18 June 2010:
Vol. 328. no. 5985, pp. 1530 - 1534
DOI: 10.1126/science.1185435
Tropical Ocean Temperatures Over the Past 3.5 Million Years

Timothy D. Herbert, Laura Cleaveland Peterson, Kira T. Lawrence, Zhonghui Liu

Determining the timing and amplitude of tropical sea surface temperature (SST) change is an important part of solving the puzzle of the Plio-Pleistocene ice ages. Alkenone-based tropical SST records from the major ocean basins show coherent glacial-interglacial temperature changes of 1° to 3°C that align with (but slightly lead) global changes in ice volume and deep ocean temperature over the past 3.5 million years. Tropical temperatures became tightly coupled with benthic 18O and orbital forcing after 2.7 million years. We interpret the similarity of tropical SST changes, in dynamically dissimilar regions, to reflect "top-down" forcing through the atmosphere. The inception of a strong carbon dioxide–greenhouse gas feedback and amplification of orbital forcing at ~2.7 million years ago connected the fate of Northern Hemisphere ice sheets with global ocean temperatures since that time.