According to a new study published in Science, researchers at Columbia University have found that carbon dioxide emissions have lowered the ocean’s pH levels at a rate unparalleled in at least the last 300 million years of our planet’s history. CO2 pollution is altering the chemistry of the oceans, and the cause of the heightened CO2 levels, the researchers note, is human activity.
Excess CO2 in the atmosphere is absorbed by the seas, where it is converted to carbonic acid, which dissolves the carbonates needed by some organisms, like plankton, corals, oysters and the tiny snails salmon eat. Coral reefs, the most bio-diverse ecosystems on the planet, form essential habitat for many marine species higher up the food chain, which makes the overall impact of ocean acidification difficult to predict.
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Lead author Barbel Honisch reported that higher levels of carbon dioxide in the atmosphere have lowered the pH of the ocean by 0.1 unit in the last century. While this amount may appear small, this rate of change is 10 times faster than the closest historical comparison from 56 million years ago during the Paleocene-Eocene era.
The Paleocene-Eocene Thermal Maximum, initiated by unknown geologic events, refers to a period when atmospheric carbon concentrations nearly doubled, resulting in a rise in global temperatures of 6 degrees Celsius (42 degrees Fahrenheit). Over a span of 20,000 years, the atmospheric concentration of carbon dioxide may have pushed pH levels down by 0.45 units. By analyzing deep sea sediments and fossil records, researchers discovered mass extinctions of marine organisms which accompanied this shift. As many as half of all species of seabed-dwelling single-celled creatures called benthic foraminifers became extinct, suggesting species higher up the food chain may also have died out.
Two other mass extinctions about 200 million years and 252 million years ago may also be linked to acidification, though there’s less fossil evidence, according to the study.
The UN’s Intergovernmental Panel on Climate Change has said ocean pH may fall another 0.3 units this century. And while ocean acidification continues to increase, the study warns that scientists may not know the full impact of a higher rate of acidification in the oceans for many years.
Honisch offers a sobering perspective on the research findings. “What we’re doing today really stands out. We know that life during past ocean acidification events was not wiped out — new species evolved to replace those that died off. But if industrial carbon emissions continue at the current pace, we may lose organisms we care about — coral reefs, oysters, salmon.”
“The current rate of CO2 release stands out as capable of driving a combination and magnitude of ocean geochemical changes potentially unparalleled in at least the last 300 million years of Earth history, raising the possibility that we are entering an unknown territory of marine ecosystem change.”
Researchers based in the United States, Britain, Netherlands, Germany and Spain contributed to the study, which was funded by the U.S. National Science Foundation.