Harvard scientists are helping show the fullest picture of how global spikes in carbon dioxide (CO2) combined to finish off the last ice age 20,000 to 10,000 years ago.

Researchers compiled ice and sedimentary core samples collected from dozens of worldwide locations, and found evidence that while changes in Earth’s orbit may have touched off a warming trend, increases in CO2 played a far more important role in pushing the planet out of the ice age.

“Orbital changes are the pacemaker. They’re the trigger, but they don’t get you too far,” said Jeremy Shakun, visiting postdoctoral fellow in Harvard University’s Earth and Planetary Science department, who led the study, the journal Nature reported.

“Our study shows that CO2 was a much more important factor, and was really driving worldwide warming during the last deglaciation,” added Shakun, according to a university statement.

Though scientists have known for many years, based on studies of Antarctic ice cores, that deglaciations over the last million years and spikes in CO2 were connected, establishing a clear cause-and-effect relationship between CO2 and global warming from the geologic record has remained difficult, Shakun said.

In fact, when studied closely, the ice-core data indicate that CO2 levels rose after temperatures were already on the increase, a finding that has often been used by global warming skeptics to bolster claims that greenhouse gases do not contribute to climate change.

To get a more accurate picture of the relationship between global temperature and CO2, Shakun and colleagues synthesized dozens of core samples - 80 in all - collected from around the world.

Armed with that evidence, they were able to sketch out how a series of factors aligned that eventually led to a worldwide warming trend and the end of the ice age.

While the research strengthens the link between CO2 and the Ice Ages, Shakun believes it also reinforces the importance of addressing CO2-driven climate change in our own time.