Ocean’s Circulation And Its Effects On Our Climate
June 7, 2012

Ocean’s Circulation And Its Effects On Our Climate

Scientists have long believed that global warming and levels of CO2 were associated. As levels of carbon dioxide increased, so too did the Earth´s temperatures. Now, paleoclimate researchers have studied ancient skeletons from microscopic plankton from the Miocene period to better understand our climate 12 to 5 million years ago. They found warmer periods and increased levels of CO2 didn´t always operate hand in hand, saying the two effects once operated independently of one another. These researchers have published their findings in this week´s issue of the journal Nature.

Petra Dekens, assistant professor of geosciences at San Francisco State University, co-authored this newly published study and says temperatures across the North Pacific during the Miocene were actually 9-14 degrees warmer than today. Yet, levels of CO2 remained low, near pre-Industrial Revolution values.

“There was a transition, from the Earth´s climate system being not as sensitive to changes in atmospheric carbon dioxide to becoming more sensitive to these changes,” Dekens said in the press statement.

“What´s interesting is that we can see this transition happening within the last 13 million years.”

This study also suggests the ocean´s circulation may have sparked the coupling between global warming and increased CO2 levels. As such, the Earth grows warmer in reaction to increasing CO2 levels.

“This work represents an important advance in understanding how Earth´s past climate may be used to predict future climate trends,” says Jamie Allan, program director in the National Science Foundation´s (NSF) Division of Ocean Sciences, according to NSF.gov.

The research team took to the ocean to look for clues about ancient Earth´s climate and atmosphere, taking samples of microscopic plankton skeletons and the sediment these microfossils were buried beneath. These recovered samples provided the first evidence that sea surface temperatures during the Miocene period were quite warmer, then gradually cooled as the period progressed. Yet, as the seas were warmer, the level of CO2 remained low.

“In the late Miocene, there must have been some other way for the world to be warm,” said Johnathan LaRiviere, research team leader at the University of California at Santa Cruz.

“One possibility is that large-scale patterns in ocean circulation, determined by the very different shape of the ocean basins at the time, allowed warm temperatures to persist despite low levels of carbon dioxide,”  LaRiviere said, speaking for the NSF.

Of course, the world´s waterways are much different than they were during the Miocene period. For instance, the Central American Seaway was open, while the Indonesian Seaway was much wider and the Bering Strait was closed. These Seaways created different boundaries around the Pacific, the world´s largest ocean. By the time the Earth had entered the Pliocene period 5 million years ago, the world´s continents and oceans very closely resembled how they look today. As the world entered this period, there was also a drop in global average temperatures, as well as an appearance of large ice sheets in the Northern Hemisphere. The world´s climate finally came into its own, and it's the same one we´ve known since the beginning of recorded time.

“This study highlights the importance of ocean circulation in determining climate conditions,” says LaRiviere´s teammate Christina Ravelo. “It tells us that the Earth´s climate system has evolved, and that climate sensitivity is possibly at an all-time high.”