Richard Norris, a geologist at Scripps Institution of Oceanography, UC San Diego, said the concentration of CO2 is one means of comparison, but what is not comparable, and more significant, is the speed at which 400 ppm is being surpassed today.
“I think it is likely that all these ecosystem changes could recur, even though the time scales for the Pliocene warmth are different than the present,” Norris said. “The main lagging indicator is likely to be sea level just because it takes a long time to heat the ocean and a long time to melt ice. But our dumping of heat and CO2 into the ocean is like making investments in a pollution ‘bank,’ since we can put heat and CO2 in the ocean, but we will only extract the results (more sea-level rise from thermal expansion and more acidification) over the next several thousand years. And we cannot easily withdraw either the heat or the CO2 from the ocean if we actually get our act together and try to limit our industrial pollution–the ocean keeps what we put in it.”