Reveals important changes in Earth’s climate roughly 5 million years ago
A paper published in the April 4 issue of Nature, one of the most prestigious science journals in the world, by Lafayette College’s Kira Lawrence and a team of researchers reveals important features of the Earth’s climate roughly 5 million years ago during the Pliocene epoch.
The Pliocene is considered one of the best analogs for determining future climate conditions because it was the most recent time when the concentration of carbon dioxide in the Earth’s atmosphere was similar to what it is today, and global average temperature were about 3 degrees Celsius warmer than now, a magnitude that matches projections for the amount of warming that should result from human-induced climate change by the year 2100.
Lawrence and her collaborators from Yale University, University College London, University of Hong Kong, San Francisco State University and University of California, Santa Cruz compiled records of sea surface temperatures going back millions of year, which were generated from chemical signatures preserved in ocean sediment cores. These data reveal three important temperature patterns during the warm period of the Pliocene: 1) that maximum ocean temperature were about the same as now; 2) that unlike today, across the tropics waters were fairly uniformly warm; 3) that the differences in temperature between high latitudes and the tropics were much smaller.
“Despite what seems to have been marginally different climate forcing during the Pliocene, the temperature patterns on the surface of the Earth were quite different compared to now,” says Lawrence, associate professor of geology and environmental geosciences at Lafayette. “There has been a tendency to focus on changes in global mean temperature as a means of comparing how similar climate was in the past to what it is now. What our study shows is the potential for climate patterns to be markedly different in a world that was not that much warmer than today’s.”
If that’s the case, Lawrence says, we could see significant changes in temperature and precipitation patterns in the not too distant future.
The research team then used climate models to explore whether or not any of the previously proposed mechanisms for the warm conditions of the Pliocene could reproduce the three characteristic features of the Pliocene temperature pattern. Their model experiments revealed that no single mechanisms could account for the observations, suggesting that a combination of factors is likely necessary to explain the warmth and climate patterns observed during the Pliocene.
Lawrence and her team suggest that in addition to higher carbon dioxide concentrations, other dynamic factors, such as diminished cloud reflectivity and ocean mixing in subtropical waters due perhaps to widespread hurricanes, must have played a role in Pliocene warmth.
Lawrence says, “Understanding the conditions and the processes controlling the climate of the Pliocene are potentially important for understanding future climate changes. To advance that objective, this study provides a synthesis view of the Pliocene temperature pattern and demonstrates that no single mechanism previously proposed can account for that pattern. These results imply that there may be some important feedbacks or other mechanism that operate in warm climate states that we don’t yet fully understand.”
For more information, contact Kira Lawrence, associate professor of geology and environmental geosciences at Lafayette, firstname.lastname@example.org; (610) 330-5194.
Higher resolution photo available.