Pace of Ocean Acidification Has No Parallel in 300 Million Years, Paper Says


A new scientific paper suggests that the ocean is acidifying at a rate that is many times faster than at any time in the last 300 million years. The change is occurring so rapidly that it raises “the possibility that we are entering an unknown territory of marine ecosystem change,” said the paper, published this week in the journal Science.

The new study, led by Bärbel Hönisch, a Columbia University paleoceanographer, does not present much new scientific evidence on the issue. Instead, it is a careful analysis of the existing evidence from decades of research on the earth’s geologic history.

That history features some fast releases of carbon dioxide into the atmosphere that in some ways resemble the current trend of release to which humans greatly contribute by burning fossil fuels today. Those historical releases warmed the planet just as it is warming now. Because much of the extra carbon dioxide released into the air gets deposited in the ocean as a mild acid, past events also caused the ocean to turn more acidic.

But as scientists have long known, and the new paper reiterates, those previous releases were usually much slower than the one occurring now. (While the present-day release of carbon dioxide is slow on a human time scale, it is essentially instantaneous on a geologic time scale.)

So scientists have been struggling to figure out whether any of those past events can serve as good analogues for the present, providing us with some sense of the environmental and biological changes that may be in store for the earth.

Slow though they may have been, some of the past events caused profound planetary change. One of them, a stupendous series of volcanic eruptions in what is now Siberia starting about 250 million years ago, put so much carbon dioxide into the air over the course of a million years that it apparently wiped out most species on earth. Life took tens of millions of years to recover.

A more interesting analogy, however, may be the Paleocene-Eocene Thermal Maximum 55 million years ago, in which a pulse of carbon dioxide from an unknown source entered the atmosphere over several thousand years. That event produced immense environmental changes and some extinctions of life in the sea, but research suggests it did not lead to mass extinctions on land.

It did produce a rapid proliferation of new species as land animals adjusted to the environmental shifts. Our own lineage, the primates, apparently blossomed during that event, filling new ecological niches.

The new paper suggests that ocean acidification is now unfolding at at least 10 times the rate that it was during the Paleocene-Eocene Thermal Maximum. Thus, the scientists conclude that no past event is likely to serve as a perfect analogue for the human release of carbon dioxide, which “stands out as capable of driving a combination and magnitude of ocean geochemical changes potentially unparalleled” in 300 million years, the paper says.

Patrizia Ziveri, a researcher from the Autonomous University of Barcelona who took part in the study, said the findings underlined the need for rapid policy action. “Considering the effects we detect through fossil records, there is no doubt that we must tackle the problem at its roots as soon as possible, adopting measures to immediately reduce our CO2 emissions into the atmosphere,” she said in a statement.