The hottest regions of the tropical oceans were one to two degrees Celsius warmer than today during a period of warmth in the Pliocene epoch, three to five million years ago, reports a paper published online in Nature Geoscience. This finding opposes previous suggestions that Pliocene tropical ocean temperatures were similar to today even though average global temperatures were three to four degrees higher.
Charlotte O’Brien and colleagues reconstructed the sea surface temperature history of parts of the tropical Indo-Pacific and Atlantic warm pools, using three indicators of past temperature recovered from marine sediments. Today, these are the warmest regions in the global ocean. They conclude that during the Pliocene, sea surface temperatures in these regions were warmer than today as would be expected in the warmer atmosphere.
In an accompanying News and Views article, Mark Pagani writes that “we are now left to explain an even warmer Pliocene world than previously assumed, even though that world was bathed in atmospheric CO2 concentrations very similar to today.”