London, July 19 : New data has suggested that ocean temperatures could have soared as high as 41 degree C during the Eocene period 55 to 34 million years ago, evidence of which might be in missing plant fossils from that period, which holds the key to how our planet will respond to global warming in the future.
The Earth went through a prolonged phase of extremely high temperatures during the Eocene, in which even the poles were ice-free.
However, there has always been some doubt about the temperatures of the tropics during this period. Most paleo-climate records show that the tropics had mean annual temperatures of 28 to 33 degree C, which is not much warmer than today.
Recently, however, better-calibrated data have suggested that ocean temperatures could have soared as high as 41 degree C.
According to a report in New Scientist, if the tropics were indeed this hot, it would solve a huge problem faced by existing climate models, including those used by the Intergovernmental Panel on Climate Change (IPCC).
Existing models have difficulty duplicating climates in which the temperature gradient from the tropics to the poles is small, as suggested by the older paleo-climate data for the Eocene.
"This cannot be explained by current-generation IPCC-class climate models, suggesting that these models lack certain mechanisms that could be important in future greenhouse climates," said Appy Sluijs, a climate scientist at Utrecht University in the Netherlands.
If the tropics really were much hotter during the Eocene, it could have serious implications for future climate change since the same thing could happen again.
"If that's the case, then we can't rely on some magical, benevolent thermostat that is just going to kick in and keep the tropics from heating up," said climate modeller Matthew Huber of Purdue University in Lafayette, Indiana.
Given what's at stake, Huber is calling for more direct evidence to help ascertain if the tropics were indeed much hotter during the Eocene.
A strong piece of evidence would be the discovery of large-scale die-offs of plants in the tropics during this period.
If ocean-surface temperatures during the Eocene were on the high end of what is suggested by paleo-climate records - 35 to 41 degree C - then temperatures in the interior of continents in the tropics would have been up to 10 degree C higher. This would most certainly have killed off any plants, according to Huber.
Huber suggests searching for fossil records of leaves from the heart of Africa and Brazil, comparing the late Paleocene (65 to 55 million years ago) and the phase that followed it, called the Paleocene-Eocene Thermal Maximum (PETM).
"The plants should be there in the late Paleocene (which was colder) and gone during the PETM," he said.