Can oceans forecast the future of climate change?

Graphic by Julia Read

A recent report by the Intergovernmental Panel on Climate Change, a global body that assesses science related to climate change, found that Earth’s temperature is projected to increase a staggering two degrees Celsius by the end of the century.

The report found that if human emissions were immediately reduced to zero, global temperature would only increase by 1.5 degrees. This reduction would lower projected species loss and extinction and reduce the number of people exposed to climate-related risks and those susceptible to climate change induced-poverty, as compared to a two degree increase, the report concluded.

“To limit warming by 1.5 degrees Celsius by 2040, there is no way to do that without global CO2 emissions reaching net zero by 2055. For context, we emit about 10 billion tons of carbon per year,” said  Jesse Farmer, a postgraduate paleoceanography researcher at Princeton University.

Farmer studies ancient ocean sediments to understand the carbon cycle and Earth’s climatic past. He recently talked about his research for a Geology Department Colloquium, a series of geology research talks held through the Pomona College Geology Department each semester.

Farmer explained that there are four main carbon reservoirs on the Earth’s surface: the atmosphere, the terrestrial biosphere, sediments, and the ocean, which is the largest reservoir.

“What’s important about the anthropogenic perturbation is that the ocean is helping us out,” he explained. “If you get rid of the ocean entirely, atmospheric CO2 levels would be much, much higher. The ocean is fundamentally absorbing carbon, from the fossil fuels that we are emitting today, and taking it out of the atmosphere. So, CO2 levels aren’t as high.”

One of the motivations behind Farmer’s research is understanding how carbon inventory in the ocean has changed in the past, particularly during a time period called the Mid-Pleistocene Transition, around 1 million years ago, where there was a profound alteration in the Earth’s climate rhythm. Farmer explained that climate rhythms over the past million years are tightly coupled to the carbon cycle and the concentration of CO2 in the atmosphere.

“If we figure out how carbon concentration has changed, we can then think about what caused it. If we can figure all this out, we might get a much better sense for how things will change in the future now that we are adding more carbon to the surficial carbon supply,” Farmer said. “Will the ocean continue to just take up carbon from the atmosphere? Will the ocean’s capacity to absorb carbon be exceeded entirely? Will it start releasing carbon back into the atmosphere?”

To gain clues about past carbon concentrations in the ocean, Farmer has turned to foraminifera, shelled ocean zooplankton about the size of a pinhead.

“They are a paleooceanographer’s best friend,” he exclaimed.

Farmer recovers sediments from the bottom of the ocean that contain fossilized shells of foraminifera that lived in the ocean hundreds of millions of years ago.

“What we can take advantage of is that forams have this beautiful carbonate shell that provides a potential archive we can use to interrogate changes in ocean chemistry,” Farmer said.

A typical day for Farmer involves dissolving these forams in acids and trying to figure out the type of trace elements present in the shells.

“Any trace element in the seawater … is incorporated into these foraminifera shells,” Farmer said. “I can measure the ratio of different trace elements in them to tell us something about past ocean chemistry, and that can tell us how much carbon [was] in the oceans in the past.”

Quantitative data from Farmer’s research suggests a fundamental increase in carbon content in the ocean 1 million years ago.

“There is an increase in the carbon inventory in the ocean that most likely came from the atmosphere, and if I just do a mass balance and say all the extra carbon in the ocean came out of the atmosphere, then we must have had to reduce CO2 in the atmosphere in order to increase carbon in the ocean,” Farmer said.

Understanding how carbon concentrations in the ocean changed 1 million years ago has plenty of implications for the climate change we are experiencing today. The time period Farmer’s research is based in spans over a million and a half years of Earth’s history.

“Even this abrupt event at the [Mid-Pleistocene Transition], which is on the order of 40-50 thousand years, is an extremely long time compared to what’s happening today,” Farmer said. “It’s not so much the magnitude of the human perturbation that matters, it’s how quickly it’s happening.”

As Farmer explained, slow changes in the carbon cycle in the past have resulted in large changes in Earth’s cycle. We have already added three times more carbon to the ocean in the past 200 years than the amount of carbon that was absorbed by the ocean during the MPT, a time period lasting thousands of years.

Farmer concluded that “even if you are not part of this field, in the future you’re going to see a lot more discussion as to what is the role of our knowledge of the carbon system.”

As global temperature increases and the effects of climate change intensify, Farmer believes one question could become prominent: Is there a way we can take advantage of what we know about that the carbon cycle to pull some amount of CO2 out of the atmosphere? His answer: We don’t know nearly enough about the system yet.

D’Maia Curry is a geology major at Pomona College. She loves dancing, reading, and looking at really cool rocks.

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