Thanks to a NASA satellite that’s been mapping the greenhouse gas carbon dioxide in the atmosphere in unprecedented detail, scientists are learning much more about how plants work, and how the land and oceans suck up and release CO2. This information could help us figure out how our world will respond to global warming.
New research shows that during the 2015–2016 El Niño, for instance, droughts, heat, and fires in tropical areas caused plants and soil on three continents to contribute to the largest growth of carbon dioxide on record. Plants use CO2 to grow, and they suck it out of the atmosphere. But during this event, because of little rain and higher than normal temperatures in South America, Africa, and Asia, some plants didn’t absorb as much CO2; others died and decomposed more quickly, releasing the carbon they’d pulled from the air. The newly observed behavior may provide clues for how the changing climate will create new feedback systems that can accelerate global warming.
These findings, published in one of five studies coming out today in Science, represent just the first batch of discoveries from a mission NASA launched in 2014. The satellite, called Orbiting Carbon Observatory-2, or OCO-2, is designed to monitor carbon dioxide in our planet’s atmosphere. CO2 levels have been increasing since the Industrial Revolution in the 1800s, and because CO2 is a heat-trapping greenhouse gas, our planet is warming up. Today, we keep pumping out huge amounts of carbon by burning fossil fuels, but about 25 percent of those emissions are absorbed by the ocean, and another 25 percent is vacuumed up by plants. Today’s papers are the beginnings of explanations about how this carbon is taken up, and if these processes will last as the world continues to warm.
“There’s a lot of uncertainty on what the world might be like in 100 years, and understanding more of what we’re seeing now can help us predict better what the future holds,” says Annmarie Eldering, the deputy project scientist for the OCO-2 mission at NASA’s Jet Propulsion Laboratory (JPL), and the co-author of a few of the studies.
The OCO-2 satellite zooms around the Earth over 14 times a day, gathering about 100,000 measurements per day — including in areas that haven’t been observed much before, like the middle of the ocean and the Amazon rainforest. Using that data, researchers put together a map of CO2 concentrations over the planet, to see how the gas is absorbed and emitted, and how it’s dispersed into the atmosphere.
One such map, described in one of the studies, shows how the Northern Hemisphere — where most continents are — is engulfed in carbon dioxide in the winter. But as the spring arrives and plants reactivate, concentrations take a nosedive. “To me, it was just like, ‘Wow!’” says Eldering. “It looked like some monster took a bite out of the carbon dioxide in those regions. I was amazed by how powerful the natural systems are.” Another study shows that the OCO-2 satellite can be used to track CO2 over really small areas, like volcanoes and cities like Los Angeles. That could be used not only to better understand city pollution, but also to predict when volcanoes will erupt.
As scientists keep delving through the first years of data, here are some of their major findings so far.
The OCO-2 satellite launched in July 2014, right before the beginning of one of the strongest El Niños ever. “It was just dumb luck,” says Scott Denning, a professor of atmospheric science at Colorado State University, who was not involved in the research. El Niño is a recurring climate pattern that brings warm waters to the tropical Pacific Ocean, affecting weather all over the globe. And the first El Niño the satellite observed was a doozy.
An extra 2.5 gigatons of CO2 was released into the air compared to 2011, when conditions were normal, one of the Science papers reported. That extra carbon, about 25 million Statues of Liberty worth of mass, came from tropical areas in South America, Africa, and Asia — where plants all reacted differently. In South America, the plants’ growth was stunted by drought, causing them to vacuum up less CO2 than usual. In Africa, the heat caused dead plants to decompose more quickly, releasing high amounts of CO2. And in Asia, drought and heat caused forest fires, which also pumped huge quantities of carbon into the air.
In another study, researchers looked at how the same El Niño affected the ocean. Although the world’s oceans suck in about 25 percent of our CO2 emissions, different oceans behave differently: while the northern Atlantic absorbs CO2, the tropical Pacific usually releases CO2, says study co-author Abhishek Chatterjee, a scientist at University Space Research Association, working at NASA Goddard. That’s because powerful winds that blow east to west across the Pacific carry deep ocean water rich in CO2 to the surface. From there, part of that CO2 is leaked into the atmosphere.
But during El Niño, those winds weaken, bringing less CO2 to the surface. That means less carbon is dispersed into the air. But how little? The rate at which CO2 leaked from the tropical Pacific dropped as much as 54 percent between March and July 2015, the first months of El Niño, Chatterjee and his colleagues found. The concentrations of CO2 then skyrocketed as plants in South America, Africa, and Asia released huge amounts of carbon as described in the other Science paper.
“This is really a first for the carbon cycle community,” Chatterjee says. Scientists have long wondered how exactly CO2 fluctuates during El Niños, what roles the land and ocean play, and these papers finally provide some answers to these questions. “Observations from OCO-2 have solved that critical scientific puzzle,” Chatterjee says.
Volcanoes and cities
The OCO-2 satellite makes such high-resolution measurements that researchers can look at CO2 concentrations over very small areas, such as a city or a volcano. CO2 over Los Angeles, for instance, was higher in the winter, when plants absorb less CO2 and more plants die, than in the summer, according to one of the Science studies. It was also higher in urban areas, where there are more cars and power plant emissions, than in suburban areas, says lead author Florian Schwandner, an analytical geochemist at JPL. The findings show that the OCO-2 satellite can quickly scan cities for pollution, complementing ground-based measurements.
The OCO-2 satellite can also be used to monitor active volcanoes, such as the Yasur volcano in Vanuatu, which constantly spews out a plume rich in CO2. The measurements suggest that Yasur is pumping out 41.6 kilotons of CO2 a day. When a volcano emits CO2, it means new batches of magma are moving toward the surface — a sign of unrest. So this new technique could be used to predict volcanic eruptions, Schwandner says. “We can’t stop a volcano, but we can evacuate people,” he says. “And the earlier we get the heads up the better.”
The OCO-2 satellite can also detect when plants take solar energy to grow, a process known as photosynthesis. During photosynthesis, plants emit a tiny amount of that energy back into the atmosphere, effectively glowing. This glow is invisible to the naked eye, but not to the OCO-2 satellite, which measures it at a much higher resolution than previous satellites like NASA’s Global Ozone Monitoring Instrument 2, according to another study published in Science.
Detecting photosynthesis is key to understand whether plants are absorbing CO2. These measurements were used in one of the two El Niño papers, to figure out that during the 2015-2016 El Niño, plants in South America weren’t absorbing as much carbon. In the future, these worldwide observations of photosynthesis can be used to improve predictions of how productive crops will be in the future, as the world warms up, Eldering says.
All these observations have one main goal: to help us better understand the planet we live in — and how it’ll change in the future. And monitoring CO2 can help us unravel the mystery. “CO2 affects climate change, but also climate change affects CO2,” Denning says. “It’s kinda of a double whammy.”
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