June 27, 2005 — New Haven, Conn. —
Assistant Professor Mark Pagani in the Department of Geology and
Geophysics at Yale and his colleagues mapped the first detailed history
of atmospheric carbon dioxide between 45 – 25 million years ago based
on stable isotopes of carbon in a National Science Foundation study
reported in Science Express.
"Through the energy we consume, each of us makes a contribution to
increasing greenhouse gasses, such as carbon dioxide and methane, in
the Earth’s atmosphere," said Pagani. "To understand the implications
of these actions for the future, scientists look to the past to gain a
better understanding of Earth’s climate system under high greenhouse
gas conditions." The findings were based on calibration of
carbon-containing compounds produced by ancient sea surface algae that
were recently isolated in deep sea drill cores.
The data indicates that between 45 – 34 million years ago the
atmospheric carbon dioxide level was up to five times greater than
today, with a sharp decrease and then stabilization to near modern day
levels between 34 – 25 million years ago.
During the early part of the Paleogene Period, from 65 – 34 million
years ago, global climates were much warmer than today with very little
ice present at the poles. The boundary of the Oligocene and Eocene
Epochs 33.7 million years ago was marked by rapid global cooling and
the formation of large continental ice sheets on the Antarctic.
"Before this study, the relationship between the global climate and
the concentration of carbon dioxide in the atmosphere during the late
Eocene and Oligocene was largely unknown," said Pagani, who is
recognized for his reconstruction of past atmospheric carbon dioxide
levels between 25 million and eight million years ago.
They also present intriguing evidence that the sharp drop in carbon
dioxide level, between 33 – 25 million years ago, prompted the origin
of economically important land plants that are sensitive to atmospheric
carbon dioxide levels, such as corn and sugarcane.
"The onset and stabilization of ice sheets at the same time as a
decline in carbon dioxide illustrates the importance of atmospheric
carbon dioxide as an agent of both climate and biological change,"
Collaborators were Brett Tipple from Yale, James C. Zachos and
Stephen Bohaty at University of California, Santa Cruz and Katherine
Freeman at Pennsylvania State.
Source : Yale University