Humankind will soon lose a great deal of vigilance over the ozone layer, which shields life on Earth from harmful solar radiation.
The impending loss of NASA’s Aura and the Canadian Space Agency’s SCISAT satellites threatens scientists’ ability to closely monitor compounds that destroy ozone and alter stratospheric circulation. With no planned missions to replace either satellite, a data desert in the stratosphere appears imminent, researchers warn in the March Bulletin of the American Meteorological Society.
“We’ve been thinking about this for years,” says atmospheric scientist David Fahey of the National Oceanic and Atmospheric Administration in Boulder, Colo., who was not involved in the assessment. “These satellites, as of today, will go dark in the absence of a torchbearer into the future.”
The satellites will sunset while the ozone layer’s recovery has unpredictably stalled over the midlatitude Northern Hemisphere. And experts warn that increasing amounts of space debris from dying satellites could unleash more ozone-depleting substances. What’s more, scientists will lose their ability to watch for harmful impacts to the ozone layer from wildfires and stratospheric aerosol injections aimed at countering climate warming.
To be clear, other instruments will continue monitoring the ozone layer itself. What will be lost is the ability to thoroughly scan the stratosphere for substances that can damage the ozone layer. “It’s like taking MRI and CAT scanning away and going back to just X-rays,” says coauthor Ross Salawitch, an atmospheric scientist at the University of Maryland in College Park. “We will know what is happening to the ozone. What we’ll lack is why.”
SCISAT took to the skies in 2003, followed the next year by Aura. Ever since, these satellites have advanced scientists’ understanding of the stratosphere and ozone layer. But by mid-2026, Aura’s solar panels will be unable to power its operations. And although SCISAT could theoretically remain in orbit until around 2035 — if no crucial hardware failures or funding issues arise — the spacecraft is already 18 years beyond its intended lifetime.
Once the satellites go dark, scientists will lose access to daily global measurements of ozone-destroying gases. These include halogenated gases such as hydrogen chloride and chlorine monoxide, as well as nitrogen oxides.
The origins of most of these gases can be traced to chemicals and materials manufactured by humans. Many of these source substances are regulated by the Montreal Protocol, an international agreement enacted in 1989 to phase out ozone-depleting substances. But without observations from both satellites, it will be more difficult to track how these substances are harming the ozone layer, Fahey says. “We’re going to lose that vigilance factor.”
What’s more, data from SCISAT and Aura revealed how smoke from the 2019–2020 Australian wildfires damaged the ozone layer, an impact that was unanticipated at the time. “We’re just at the beginning of trying to understand how that happens,” says atmospheric chemist Lyatt Jaeglé of the University of Washington in Seattle.
As blazes are expected to become more intense and frequent due to climate change, some researchers have proposed that wildfire emissions could have increasingly significant effects on stratospheric ozone. And large-scale injections of stratospheric aerosols — a proposed technique to mitigate climate warming by reflecting sunlight back into space — could have effects similar to a volcanic winter. That means the aerosols could potentially damage the ozone layer over large portions of the globe. The loss of the ability to monitor these impacts is a major concern, Salawitch, Fahey and Jaeglé agree.
Two potential successor missions are being considered by NASA and the European Space Agency.
One is the Changing-Atmosphere Infra-Red Tomography Explorer, or CAIRT, a concept the ESA is weighing for its next Earth Explorer mission. The satellite would provide global observations of ozone, water vapor, aerosols and ozone-damaging compounds. A decision will be announced later this year, with plans to launch the selected mission around 2032.
Meanwhile, NASA is considering the Stratosphere Troposphere Response using Infrared Vertically-resolved light Explorer, or STRIVE. This satellite would wield Aura’s monitoring capabilities and then some, providing enhanced resolution and greater coverage, says Jaeglé, who is lead investigator of the mission’s science team. A decision could be made later this year, with a potential launch in 2030 or 2032.
“If either one of these goes forward, then that’s obviously good news,” Salawitch says. “We’d like to continue to be diagnosing the patient.”