InitiativesNewsMarketsScienceGet Involved

Read Our Newsletters For the latest ocean news, subscribe to Ocean Update and our other free newsletters.

Other Ocean Voices>>
Reflections from Marine Scientist Ken Caldeira

Will We Let Corals Go the Way of the Dinosaurs?

Ken CaldeiraJosh Tickell

“Coral reefs could be just the first major ecosystem type to be lost, with many others ready to fall like dominos behind them.”

—Ken Caldeira

My passion for researching corals, then ocean acidification and now alternative energy approaches began with a look at the age of dinosaurs, 65 million years ago. My Ph.D. dissertation was largely about the stabilization of ocean chemistry after a meteorite killed off the dinosaurs along with most marine species. Organisms that made shells or skeletons out of calcium carbonate such as plankton and corals were particularly hard hit. It seems as if it took about 20,000 years for the ocean’s chemical balance to be restored, but carbonate-shelled plankton took about 500,000 years to rebound and it took about two million years for coral reefs to become widespread once again.

Coral in the Great Barrier Reef

In December 2009, Caldeira led an expedition to One Tree Island near Australia's Great Barrier Reef to investigate how rates of coral growth have changed during the past few decades. Preliminary results indicate that coral skeletal material is being added to the reef at less than half the rate measured four decades ago. Ken Caldeira

About a decade after I graduated, I was working at a Department of Energy laboratory investigating the possibility of storing industrial waste in the form of carbon dioxide in the deep sea. As part of this program, scientists compared the effects of high carbon dioxide concentrations that would result from concentrating carbon dioxide from power plants with lower concentrations of carbon dioxide absorbed from the atmosphere and with the even lower concentrations that would have been produced naturally. One of the surprises of this research was how sensitive many marine organisms were to additions of carbon dioxide. Not only were they harmed by the high concentrations that would occur from the power plant scheme, they were also harmed by the lower atmospheric concentrations that the ocean would absorb in the coming decades with a continuation of recent trends in carbon dioxide emissions.

Because of my work studying the time of dinosaur extinction, I knew that given this scenario, the ocean would take tens of thousands of years to recover chemically and could take hundreds of thousands or even millions of years to regenerate biologically. (I say "regenerate" rather than "recover" because we will never recover life that has become extinct. While new life forms will evolve in the fullness of time, the time scales for evolutionary regeneration of biologically diverse ecosystems are much longer than all of human history.) If we do not reverse current trends in carbon dioxide emissions soon, we will cause the biggest and most rapid change in ocean chemistry since the extinction of the dinosaurs. I believe that the great mass extinctions in the deep geologic past were the only times in Earth’s history in which ocean chemistry changed as much or as fast as what we have the potential to do this century.

Taking ocean water samples
Caldeira's team (including post-doctoral researcher Kenny Schneider) took seawater samples from around One Tree Island so that their carbon dioxide concentration could be measured back in the lab. Ken Caldeira

Mike Wickett and I wrote up the results of our work and submitted it to the journal Nature. That paper, published in 2003, popularized the term "ocean acidification." Since that time, we have been engaged not only in modeling and fieldwork to test the effects of ocean acidification but also trying to get the word out about what it is and what it will do to the ocean.

In our modeling work, we have explored issues such as what do different atmospheric carbon dioxide stabilization levels mean for ocean chemistry, how do climate change and ocean acidification interact to affect ocean chemistry, and what do ocean chemistry changes mean for the future viability of coral reefs?

During the past few years, we have also conducted fieldwork in Australia's Great Barrier Reef. We have been measuring the water chemistry in coral reefs, including those at One Tree Island and Lizard Island, and using these measurements to infer the growth rate of these reefs. Our preliminary data indicates that growth of the reef at Lizard Island has slowed about 40 percent since the late 1970s. We believe that most of this decrease is due to ocean acidification, but more work is needed to test this assertion.

C02 Graphs

If current carbon dioxide emission trends continue, by mid-century, no ocean water with the kind of chemistry that can sustain coral reef growth will exist. (Magenta dots represent coral reefs and colors represent how conducive chemical conditions are for forming coral reefs.) Cao and Caldeira (2008)

Coral reefs have been around for many millions of years. What we do in the next decades could cause coral reefs to disappear from the Earth for a long, long time. It seems incredible to me that humans could be so stupid as to destroy an entire collection of ecosystems that have been so robust for so long. It says something very sad about our stewardship of this planet. Coral reefs could be just the first major ecosystem type to be lost, with many others ready to fall like dominos behind them.

Economists tell us it would cost just a small percentage of our wealth to develop energy and transportation systems that do not emit carbon dioxide to the atmosphere. We can do this. It is within our technological capability. And next century, we will start running out of fossil fuels and we will have to move to new energy sources anyway. I have hope that we will have the wisdom to make this transition this century instead of next, and save coral reefs and other marine ecosystems by so doing.

But these kinds of changes to our energy and transportation systems require systemic changes at the policy level. To get people to understand the power of ocean acidification to alter our planet, I have testified before Congressional committees several times, given briefings to members of Congress and their staffs, spoken at many meetings, been on the radio and TV, appeared in documentary films and so on. We must make our views known to those elected, and make them known repeatedly. If enough of us do this often enough, our elected officials will develop the political courage to do what is right for the world and its ocean.


Ken Caldeira is a staff scientist at the Carnegie Institution, where his job is “to make important scientific discoveries.” He also serves as a professor (by courtesy) in the Stanford University Department of Environmental Earth System Science.

Caldeira is the lead author of the 2007 U.S. “State of the Carbon Cycle Report” and was chosen to be coordinating lead author of “Ocean Storage,” an IPCC report on carbon storage in the ocean. Caldeira was invited by the National Academy of Sciences Ocean Studies Board to deliver the 2007 Roger Revelle Lecture, “What Coral Reefs Are Dying to Tell Us About CO2 and Ocean Acidification.” In 2010, Caldeira was elected a Fellow of the American Geophysical Union.

Caldeira’s work has been discussed widely by major media outlets, including The New York Times, The Washington Post, Los Angeles Times, Time Magazine, NPR and BBC World Service Radio. See Ken Caldeira talk about the impacts of ocean acidification on “Good Morning America” >>