Why NASA’s New Climate Satellite is Studying Clouds and Phytoplankton

If you’re trying to spot a phytoplankton, it pays to get exceedingly close. Among the smallest life forms inhabiting both fresh and marine water, phytoplankton can measure as little as one micrometer—or one millionth of a meter. But little things can have a big impact. Blooms of phytoplankton, which are actually a form of microalgae, can spread hundreds of square miles, sometimes doing disastrous damage to fisheries, beaches, drinking water supplies, and entire aquatic ecosystems. To track so sprawling a scourge, you want to stand at a distance—675 km (420 mi.) worth of distance. That’s the altitude at which NASA’s new PACE satellite—short for Plankton, Aerosol, Cloud, and ocean Ecosystem— will orbit, after its planned launch on Feb. 6. 

Formally authorized in 2015, PACE will continue more than two generations’ worth of work NASA began in 1978 when it launched the Nimbus-7 satellite, the first ever spacecraft built to observe phytoplankton in the ocean and study its broader role in influencing the environment. But befitting a modern era in which we know so much more about environmental science as a whole and climate change in particular, PACE is a smarter, nimbler ship, one that will take the pulse of the planet in two important ways.

The first will directly address the phytoplankton question, and for government, industry, and environmental scientists, that’s important for a number of reasons. The great living carpets can sometimes be beneficial—absorbing carbon from the atmosphere and fixing it at the base of the food chain, where other, larger organisms can have at it. But toxins produced by the algae can also kill fish and other aquatic life, and in humans can lead to diarrhea, paralysis, dizziness, and memory loss, as well as abnormal liver function, vomiting, and numbness.

“We need eyes in the sky on this because [phytoplankton] grow very quickly, on a scale of hours to days,” says Jeremy Werdell, project scientist for the PACE mission. “They’re also in a fluid that’s rotating and three dimensional, so if you don’t see them today, chances are they’ll be there tomorrow.”

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Scanning for phytoplankton isn’t all PACE will do. A second, interrelated environmental factor, one that can affect climate change, is atmospheric aerosols—floating clouds of wildfire smoke, desert dust, volcanic ash, urban industrial haze, and even marine salt that has evaporated with ocean water and taken to the skies. Aerosols create a sort of floating shadow, one that, depending on their color, composition, and particle size can either absorb incoming solar energy—thus exacerbating global warming—or reflect it back to space, thus lowering the thermometer.

“I wouldn't use the term greenhouse effect,” says Werdell. “That's typically reserved for gasses, not particles. But the principle is the same in the sense that some balance of radiation is involved.”

PACE, which will go aloft aboard a SpaceX Falcon 9 rocket, with launch scheduled for Feb. 6 at 1:33 AM EST, is a relatively small machine as satellites go—weighing in at 1,700 kg (3,750 lbs) and measuring 1.5 m (4.9 ft.) tall. NASA could get away with keeping PACE compact because the satellite carries only two pieces of scientific hardware: an ocean color instrument (OCI) and a multi-angle polarimeter.

As its name suggests, the OCI is designed to measure the color of ocean water, making hair’s-breadth distinctions between various wavelengths on the spectrum to determine the chemical makeup of different regions and, in turn, the types of organisms that call those areas home, particularly various types of phytoplankton. Different species of the algae come in different shades, typically green or blue, but also, most dangerously, red. The latter is capable of producing so-called red tides, which release highly persistent toxins that move up the food chain as smaller fish consume them, bigger fish eat the smaller fish, and on and on. That, of course, is assuming the smaller fish survive, and depending on the concentration of toxins they consume, often they don’t. One red tide off of Florida in 2021 left 600 tons of dead fish on the Tampa Bay beaches. 

“PACE measures the full spectrum of color,” says Werdell, “from the ultraviolet to the near-infrared. That's new information that allows us to not just say we see phytoplankton, but what community of phytoplankton they are.”

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Distinguishing the organisms is important because phytoplankton not only have varying toxicity levels but varying metabolisms and sizes. Gathering this data will help scientists understand how emissions are trapped or released by the oceans. Some phytoplankton absorb more carbon than others—sopping it up from the atmosphere and reducing its ability to lead to global warming; some are larger—and thus sink faster and farther—sequestering the carbon they collect deeper in the water column. Phytoplankton also release gasses into the air, giving micro-droplets of atmospheric water something around which to nucleate, and leading eventually to the formation of clouds. Those, in turn, reflect away planet-heating sunlight. “The organisms are really important pieces of the puzzle,” says Werdell. The longer term goal is to learn more about the ocean-atmosphere gas-and-cloud exchange cycle and better grasp how it changes our climate. 

The polarimeter studies the other piece, looking at the aerosols in the atmosphere—principally by measuring the oscillation of sunlight as it passes through the air. That’s an essential—and at the moment incomplete—area of research. Like most scientific graphics, the ones published by the United Nations’ Intergovernmental Panel on Climate Change (IPCC) include so-called error bars to indicate the degree of uncertainty in any set of data. “The IPCC has figures that break down different contributions of things that can warm and cool the atmosphere,” says Werdell, “and right now, the biggest error bars are on anthropogenic aerosol distributions.”

He and the rest of the PACE team aim to fix that, collecting data that will help environmental scientists study aerosols and gather clues to determine the pace and severity of future climate change. “By making these measurements,” Werdell says, “we can understand how different components of the atmosphere are interacting—with some things warming and some things cooling. It's really, really important to know all of this.”