To the editors:

Marcia Bjornerud has written a tour de force on the history and chemistry of the oceans. She ties many aspects of the world’s seas together in a thoughtful narrative. There are, however, a few subjects on which I believe some comments are needed.

Bjornerud asserts that “leakage of carbon from the surface into the deeper ocean is, in fact, essential for climate regulation” and that “this process, known as the carbon pump, has partly offset anthropogenic increases in CO₂ arising from the combustion of fossil fuels.” No evidence can be found in the geological record going back 500 million years that the oceans have regulated the climate by absorbing CO₂. During this period, there is little correlation between atmospheric CO₂ levels and global temperature. There is no support for a causal relationship.

During this 500-million-year history, atmospheric CO₂ has declined from at least 6,000 parts per million (ppm) to 180 ppm. It reached its lowest level during the last major glaciation, 20,000 years ago. Far more CO₂ has been sequestered into sediments as fossil fuels and carbonate rocks, such as limestone, than has been released back to the atmosphere. If this process had continued without anthropogenic emissions, CO₂ would eventually have been reduced to lower than 150 ppm, leading to the eventual death of plant life. In this light, emissions can be seen as inadvertently rescuing life on earth from an early demise due to continued sequestration of an essential ingredient for all life.¹

Even at the present 415 ppm, of which 135 ppm are due to industrial emissions, CO₂ is still a limiting factor for the growth of most plants, including farm crops and trees. The anthropogenic increase in CO₂ has raised crop production globally by 15 to 30 percent since 1900. Field experiments show that the expected increase in the next 100 years will have an even greater impact.² It is standard procedure for commercial greenhouse growers to elevate CO₂ to 800­–1200 ppm, increasing growth and yield 20–50 percent.³

Bjornerud also asserts that “excess CO₂ in seawater can eat away at the shells of the tiny calcitic organisms that help to sequester carbon in mineral form.” She refers to the contention that higher CO₂ levels in seawater will result in ocean acidification that harms aquatic species, especially those that produce calcium carbonate from CO₂ and calcium to build protective shells. There is no evidence to support this hypothesis. Marine and freshwater calcifying species survive in a wide variety of pH values, including freshwater species of clams, mussels, and crayfish that calcify in the acidic range at pH 6 and lower.⁴

There is no conceivable atmospheric CO₂ concentration that will result in offshore ocean pH becoming lower than an alkaline 7.5, let alone neutral 7.0, in the foreseeable future.⁵ Many of the calcifying species evolved when atmospheric CO₂ was 4,000 ppm or higher. These include the microscopic phytoplankton coccolithophores, the zooplankton foraminifera, the molluscs, marine arthropods, and corals. It is primarily these species that have removed large amounts of CO₂ from the oceans in order to armor themselves with shells. Human emissions of CO₂ have inadvertently reversed the worrisome depletion of CO₂, the primary food for all carbon-based life on earth.

In her final paragraph, Bjornerud states, “All the mass extinction events evident from the fossil record have been linked to variations in ocean chemistry,” and that “the demise of the dinosaurs, for example, can be attributed in large part to oceans poisoned by the constituents of the carbon and sulfur-rich rocks vaporized by the Chicxulub impactor.” The cause of the Permian extinction is widely contested and there is no consensus on any of the suggested explanations. The only extinction for which there is relatively good evidence is that of the dinosaurs at 65 million years BP, which was coincident with a large asteroid striking the Yucatan peninsula. It is surmised that the asteroid penetrated the earth’s crust. This caused a vast amount of material to be thrown into the stratosphere, where it remained for years, blocking the sun, ending most photosynthesis, and cooling the earth until it cleared. It is difficult to imagine how a change in ocean chemistry could eliminate all the terrestrial dinosaurs in addition to the marine species. It is not difficult to imagine that both terrestrial and marine species would die out for lack of photosynthesis and the food it provides.

Bjornerud concludes, “For this reason, some of the changes in ocean chemistry observed during the Anthropocene ought to give pause. The magnitude of these changes is comparable to the Great Dyings of the geologic past.” It should be noted that the proposal to adopt the term “Anthropocene” has not yet been approved by the International Commission on Stratigraphy, which oversees the official geologic time chart.⁶ On the question of CO₂ emissions, there is simply no possibility that current emissions could make the oceans toxic for marine life.