Greenhouse gases were the main driver of climate throughout the warmest period of the past 66 million years, providing insight into the drivers behind long-term climate change.
Greenhouse gases were the main driver of climate throughout the warmest period of the past 66 million years, providing insight into the drivers behind long-term climate change.
Antarctica and Australia separated around the end of the Eocene (56 to 22.9 million years ago), creating a deep water passage between them and changing ocean circulation patterns. Some researchers believe these changes were the drivers of cooling temperatures near the end of the Eocene "hothouse" period, but some think declining levels of carbon dioxide were to blame.
If the cooling had been caused by changes in ocean circulation, regions around the equator would have warmed as the polar regions cooled, shifting the distribution of heat on Earth. But changing the concentration of greenhouse gases would affect the total heat trapped in Earth’s atmosphere, causing cooling everywhere (including in the tropics), which is what the researchers found. The findings were published in the journal Nature.
“The synchronized evolution of tropical and polar temperature we reconstructed can only be explained by greenhouse gas forcing,” said Margot Cramwinckel, a Ph.D. candidate at Utrecht University in the Netherlands and first author of the paper. “Our findings are uniquely compatible with the hypothesis that the long-term Eocene cooling was driven by greenhouse gases. This greatly improves our understanding of the drivers behind long-term climate change, which is important in order to predict the development of future climate change.”
Read more at Purdue University
Image: Sediment cores drilled from the JOIDES Resolution helped researchers create a reconstruction of past climate. (Photo by the International Ocean Discovery Program/JOIDES Resolution Science Operator)
