Past "greenhouse" episodes on Earth left the world with few large reefs, a poorly oxygenated ocean, tropical surface waters like a hot tub and food webs that did not sustain the abundance of large sharks, whales, seabirds, and seals of the modern ocean, say researchers at the Scripps Institution of Oceanography at the University of California, San Diego.
If greenhouse gases stay on a rising path at current accelerating rates, they said, this kind of "greenhouse ocean" could reappear in the future.
Their projections are based on what is known about the "greenhouse world" of 50 million years ago, when levels of greenhouse gases in the atmosphere were much higher than those that have been present during human history, they said.
However, at its current pace, Earth could recreate the CO2 content of the atmosphere in that world in just 80 years, researchers said.
A well-studied event known as the Paleocene-Eocene Thermal Maximum 56 million years ago, can serve as a guide to predicting what may happen under current climate trends, they said.
If fossil fuel use stays on its current trajectory until the end of this century, the climate effects will begin to resemble those of the PETM, with major ecological changes lasting for 20,000 years or more and a recognizable human "fingerprint" on Earth's climate lasting for 100,000 years, Scripps paleobiologist Richard Norris said.
"In many respects the PETM warmed the world more than we project for future climate change, so it should come as some comfort that extinctions were mostly limited to the deep sea," he said. "Unfortunately, the PETM also shows that ecological disruption can last tens of thousands of years."