In the past, studies of large-scale changes to the Earth’s oceans have been restricted both by the limited nature of physical sampling and the reality that often these changes occur over great lengths of time.

A 2012 paper published in the journal Science, “The Geological Record of Ocean Acidification,” takes a new approach by examining the geological record to determine levels of atmospheric carbon dioxide, global temperatures and ocean acidification over the past 300 million years. The goal of the study — which was the combined work of scientists from nearly 20 research universities — was to find periods of the Earth’s history that are analogs for current and future global conditions.

Findings of the paper include:

• The current rate of ocean acidification is faster than at any time in the past 300 million years.
• The most recent de-glacial transition phase, while similar in temperature and increases in CO₂ levels, was “two orders of magnitude slower than current anthropogenic change.”
• The period 56 million years ago known as the Paleocene-Eocene Thermal Maximum was determined to be the closest future analog. This period of sustained CO₂ release was associated with a decline in ocean pH of between 0.25 and 0.45 units. However, current acidification is occurring at almost 10 times this rate.
• Historically sustained periods of acidification and CO₂ increase — which were similar but not as extreme as the last 1,000 years — have led to the collapse of coral reefs and, in one instance, to the extinction of 96% of marine life.

The authors conclude that the geological record reveals that “the current rate of [CO₂] release stands out as capable of driving a combination and magnitude of ocean geochemical changes potentially unparalleled in … Earth history, raising the possibility that we are entering an unknown territory of marine ecosystem change.”

In related research, a 2012 study published in Climatic Change estimates that ocean acidification could lead to economic losses for the shellfish industry in excess of $100 billion over the course of this century.

Tags: science, greenhouse gases, global warming, oceans