Scientists believe that carbon dioxide has played an instrumental role in determining global weather patterns by tying together the ice age of the Northern Hemisphere and the evolving climate in the tropics 2.7 million years ago.

Researchers at Brown University in Rhode Island examined sedimentary cores taken from the ocean floor at four locations: the Arabian Sea, The South China Sea, the eastern pacific and the equatorial Atlantic Ocean.

What they found was that climate patterns in the tropics have evolved in tandem with the Ice Age cycles for the past 2.7 million years. The scientists focused on tropical ocean surface temperatures during this period because they dictate the amount of rainfall worldwide as well as the concentration of water vapour in the atmosphere.

They found that 2.7 million years ago, tropical ocean temperatures fell by one to three degrees during each Ice Age, while ice sheets increased in size in the Northern Hemisphere.

"The tropics are reproducing this pattern both in the cooling that accompanies the glaciation in the Northern Hemisphere and the timing of those changes," said Timothy Herbert of Brown University and the lead author. "The biggest surprise to us was how similar the patterns looked all across the tropics since about 2.7 million years ago. We didn't expect such similarity."

The researchers also studied cores taken in Antarctica. From these, they theorized that carbon dioxide levels dropped by 30 per cent during each global cycle, meaning it was absorbed by the oceans during each Ice Age.

"It seems likely that changes in carbon dioxide were the most important reason why tropical temperatures changed, along with the water vapor feedback," Herbert said.

The study was published in the journal Science on Friday.