David W. Brown offers this updated look at the use of satellite technology for a key metric:
A Security Camera for the Planet
A new satellite, funded by a nonprofit, aims to pinpoint emissions of methane—a gas that plays a major role in global warming.
When his phone rang, Berrien Moore III, the dean of the College of Atmospheric and Geographic Sciences at the University of Oklahoma, was fumbling with his bow tie, preparing for a formal ceremony honoring a colleague. He glanced down at the number and recognized it as nasa headquarters. This was a bad sign, he thought. In Moore’s experience, bureaucrats never called after hours with good news.
For roughly six years, Moore and his colleagues had been working on a space-based scientific instrument called the Geostationary Carbon Cycle Observatory, or GeoCarb. nasa had approved their proposal in 2016; it was now 2022, and GeoCarb was being built by Lockheed Martin, in Palo Alto, California. Once it was in space and mounted to a communications satellite, GeoCarb would scan land in the Western Hemisphere continuously in strips, taking meticulous measurements of three carbon-based gases: carbon dioxide, carbon monoxide, and methane. It would give scientists a detailed view of the carbon cycle—the process by which carbon circulates through the Earth’s forests, lakes, trees, oceans, ice, and other natural features.
An off-kilter version of this cycle, altered by human activity, is warming the planet; understanding its workings is vital for comprehending climate change. But scientists see the carbon cycle less clearly than they need to. nasa operates two Orbiting Carbon Observatories, which can detect carbon dioxide, but neither can see methane—a version of carbon that, in the short term, has more warming potential than CO2. There are a few methane-aware assets in space, among them tropomi, which was developed by the European Space Agency and the Netherlands Space Office, and GHGSat, a constellation of nine small spacecraft owned by a private company. Atmospheric scientists also study methane using planes with special sensors. But these instruments offer only zoomed-out and zoomed-in perspectives on methane; using them to help understand the carbon cycle is like trying to drive from Boston to New York by consulting only Google Earth and Google Street View. What’s needed is a medium-scale view—the atmospheric equivalent of Waze.
Our relative blindness to methane emissions is particularly worrisome. Methane has warmed the Earth by about half a degree Celsius since the Industrial Revolution, and could add nearly another degree to the temperature by 2100; by one estimate, readily available methane-reduction measures, if they were introduced in the next decade, could reduce warming by some fraction of a degree by midcentury, and perhaps by a half-degree by its end. Such a change could be enough to avert a substantial amount of climate disruption. But mitigation is made more difficult because regulators and watchdogs have limited knowledge of where the methane is coming from and why.
There are different ways to tackle these problems. MethaneSAT, a satellite being developed by the nonprofit Environmental Defense Fund, aimed to focus exclusively on methane, identifying and characterizing sources of emissions around the world. Moore’s project, GeoCarb, would provide researchers with a continuously updated map of greenhouse gases in the Western Hemisphere, helping them answer important questions about the carbon cycle more generally. (Why do oceans and tropical forests absorb more carbon under different climate conditions? How do phenomena such as California wildfires and El Niño and La Niña affect the flow of carbon?) If both projects succeeded, they would offer unprecedented views, at useful scales, of processes fundamental to climate change.
In Oklahoma, Moore set aside his bow tie and answered the phone. He recognized the voice of Karen St. Germain, the director of nasa’s Earth Science Division. Moore’s intuition had been correct: GeoCarb was being cancelled. St. Germain explained that the mission was twice over budget and two years late. nasa had also recently announced that emit—an instrument on the I.S.S. that is creating a mineral map of Earth’s arid regions—could detect extremely large methane emissions. emit, Moore felt, was a way for the agency to check the methane box on the cheap. But its data, he believed, would be of limited use.
Moore hung up the phone, frustrated and angry about the blow to his own plans. But he was also concerned. By cancelling GeoCarb—its only spacecraft in active development designed to detect methane, and an instrument key to making major advances in our understanding of the carbon cycle—nasa had left scientists with less climate data, and policymakers with fewer options. For methane, much of the burden now rested on the Environmental Defense Fund. But could a nonprofit organization that had always been earthbound really succeed in designing its own satellite and getting it into space?
Virtually all life on Earth depends on the carbon cycle. While it’s alive, a tree pulls carbon dioxide from the air; when the tree dies, oxygen-breathing bacteria break it down, releasing its stored carbon as carbon dioxide. Ideally, an adjacent tree takes in the newly liberated CO2; when that tree falls, another absorbs the molecules. It’s an elegant system.
The carbon cycle goes on even in places that are oxygen-deprived. Sometimes, a tree falls into a marsh, or other similar environment; beneath the surface or underwater, there isn’t enough oxygen for aerobic bacteria to do the work of decomposition. Instead, anaerobic microbes called methanogens turn the tree’s carbon into methane, a molecule of one carbon atom and four hydrogen atoms—CH4, rather than CO2. Slowly, this methane seeps out of the muck or water and back into the air, where it survives for about a dozen years until it’s broken down into CO2.
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