Scripps Research Gives Tiny Phytoplankton a Large Role in Earth’s Climate System

Study, which shows microscopic plants keep planet warm, offers new considerations for iron fertilization efforts in the oceans

The ecological importance of phytoplankton, microscopic plants that free-float through the world’s oceans, is well known. Among their key roles, the one-celled organisms are the major source of sustenance for animal life in the seas.

Now, in a new study conducted by researchers at Scripps Institution of Oceanography at the University of California, San Diego, our understanding of the significance of phytoplankton has been taken to a new level.

Robert Frouin and Sam Iacobellis have argued in a paper published in the Journal of Geophysical Research that phytoplankton exert a significant and previously uncalculated influence on Earth’s climate.

The Frouin-Iacobellis study uses satellite imagery to show that phytoplankton, which are said to inhabit three-quarters of Earth’s surface, hold a fundamental warming influence on the planet by capturing and absorbing the sun’s radiation. The authors show that radiation that otherwise might be reflected back to space is absorbed by phytoplankton and results in a global climate warmer by 0.1 to 0.6 degrees Fahrenheit (compared with an open seawater scenario without phytoplankton).

“Our paper shows that if we did not have phytoplankton in the ocean, we would have a cooler climate. This is a problem that we have to look at more carefully if we want to conduct more accurate predictions of climate change,” said Frouin, a research meteorologist at Scripps. “Certainly the effect we have shown from phytoplankton is not negligible, so we need to look at it closely.”

“Eventually, I hope that incorporating this new information will lead to better predictions of future climate, and that will help policymakers make more far-sighted decisions,” said Iacobellis, a member of the Climate Research Division at Scripps.

Furthermore, in the paper Frouin and Iacobellis argue that the impact of phytoplankton extends beyond its warming influence. Changes in Earth’s surface reflection caused by increases or decreases in phytoplankton concentrations may significantly affect the interactions of the planet’s climate system with human-produced concentrations of greenhouse gases and aerosols.

They also argue that the climatological significance of phytoplankton is increased or decreased from region to region, since the magnitude of phytoplankton concentrations ultimately will dictate the strength of their warming influence.

The new findings, constructed through modeling designs and satellite imagery data from the Coastal Zone Color Scanner, also hold implications for ongoing discussions of reducing global warming through ocean “fertilization.” Such efforts have held that global warming may be decreased by fertilizing the oceans with iron, which would lead to an increase in the ocean’s biological pump. Through such an increase, the argument holds, phytoplankton would be able to draw carbon dioxide out of the atmosphere and therefore reduce global warming.

Frouin and Iacobellis, however, believe their new findings may run counter to those arguments.

“We are saying that if you increase the amount of phytoplankton in the ocean, which would probably be a consequence of this iron fertilization, instead you would contribute to warming the ocean by absorbing more radiation,” said Frouin.

“You would exert a negative feedback because you would go in the opposite direction of the effect that you want, which is to decrease global warming,” said
Iacobellis. “Think about this: If you fertilize the ocean you will take up more carbon dioxide, but you are going to get more phytoplankton. Our numbers at least give a start to rough calculations of how much of your initial decrease in temperature is going to be negated by our increase. We’re not saying that (iron fertilization) idea should be off the table, but this new information is something that should be considered.”

Last year Frouin and Iacobellis published a study detailing the extent to which ocean whitecaps influence climate by reflecting solar radiation from Earth’s surface. They say the consequences from the new phytoplankton study are an order of
magnitude larger.

The results were calculated through average impacts of phytoplankton on a broad, global scale, but the authors say detailed analyses will show varying results due to the fact that various types of phytoplankton species absorb more radiation than others. Some, in fact, reflect the sun’s radiation rather than absorb it. Also to be determined are the complex biological feedback consequences that lead to more or less phytoplankton in certain areas.

“This just shows how intricate the climate system is,” said Iacobellis. “It’s like a ball of yarn all pushed together. It’s difficult to unpiece the climate or put together what might happen in the future when all these things act together. One by itself may not be that important but when thousands of these small things act together, then?”

The research was supported by NASA, the Department of Energy, and the California Space Institute.