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In August, as wildfires crept close to the historic Lick Observatory near San Jose, California, Claire Max watched as live webcams showed flames edging toward observatory buildings and several telescopes. In the end, firefighters kept the flames at bay. Although two unused buildings were destroyed and several houses were damaged, the working telescopes only had a bit of ash on the mirrors. “We really lucked out,” says Max, director of the University of California Observatories, which runs Lick. Coastal California has always experienced cycles of drought and fire, she says. “But it’s perfectly plausible for people to say global warming didn’t make it any better.”

Astronomers have a climate problem. Not only is global warming increasing the frequency of wildfires and the strength of hurricanes that physically threaten observatories, but a changing climate could mar their views by bringing higher temperatures, humidity, and turbulent air closer to their mountaintop perches. Astronomers are also adding to the climate problem themselves, with long flights to remote facilities and meetings and heavy use of energy-hungry supercomputers for cosmic simulations. “We’re part of the problem, not of the solution,” says Leo Burtscher of Leiden University.

Those concerns were cast in sharp relief by six papers published last month in Nature Astronomy. One, on the carbon costs of meetings, emerged directly from the 2019 European Astronomical Society (EAS) meeting in France, which took place during a record-breaking heatwave when temperatures exceeded 45°C. “We were sitting with no air conditioning, sweating through all these interesting talks,” Burtscher says. Discussions turned to climate change and the carbon emitted getting everyone to the meeting, and they inspired Burtscher and his colleagues to size up the meeting’s travel emissions. They added up to nearly 1900 tons of carbon dioxide (CO₂) equivalent or about 1.5 tons per delegate—roughly the same as emitted by an average resident of India in a whole year.

Other fields of science doubtless generate similar emissions from large meetings, but astronomers’ work habits are carbon heavy as well. Another of the six studies found that Australian astronomers each produced 37 tons of CO₂ equivalent per year, of which 60% came from supercomputer usage. “We were surprised how big the supercomputers were. Everyone thought flights would dominate,” says lead author Adam Stevens of the University of Western Australia, Perth. A similar analysis in Nature Astronomy of the 2018 emissions from Germany’s Max Planck Institute for Astronomy (MPIA) showed lower emissions overall (18 tons per astronomer), to which flights were the biggest contributor. The authors say the greater use of renewable energy in Germany may explain some of that difference, but the MPIA astronomers still generated three times the emissions of a typical German.           

The climate that astronomers are helping warm is in turn threatening their view of the sky. In another of the papers, MPIA’s Faustine Cantalloube and colleagues went through 30 years of weather records from the Paranal Observatory in Chile, operated by the European Southern Observatory (ESO). They found average temperatures there had risen by 1.5°C, more than the 1°C average global rise since preindustrial times. Cantalloube says that’s already causing trouble for Paranal’s Very Large Telescope—four separate 8.2-meter reflectors. During the day, cooling systems kick in to keep temperatures inside the telescope domes the same as that of exterior air at sunset, to avoid temperature differences that create turbulence when the dome is opened. When daytime temperatures exceed 16°C, the system struggles. “The dome cooling is not good enough,” Cantalloube says. “At the time it was built in the 1990s, we were not thinking that [the temperatures] would be so high by 2020.”

The hike in temperature has also increased turbulence in the surface layer, the air a few tens of meters above the telescopes. Surface layer turbulence has risen since the 1980s, the researchers found, and although it hasn’t yet affected observing, it is worrying, Cantalloube says. “There is clearly something going on very close to the ground,” she says.

A hotter climate is expected to raise humidity levels as well, which can lead to increased cloud cover—an obvious problem for astronomers. The water vapor itself can block infrared and microwave radiation, the focus of the Atacama Large Millimeter/submillimeter Array (ALMA), also in Chile. So far, moisture has not increased at Paranal, Cantalloube’s analysis shows, or at ALMA, according to a separate study. Climate models are not yet fine-grained enough to predict future moisture trends at the observatories. “We will have to see if climate change will drive more humidity into the region,” says ESO atmospheric scientist Angel Otárola.

Astronomers are now taking steps to reduce their carbon footprint. In another of the six studies, Simon Portegies Zwart of Leiden University calls for changes in computing strategy. Astronomers should avoid traditional computers and instead use ones that rely on more efficient graphical processor units, Zwart says, although they are harder to program. Astronomers should also abandon popular programming languages such as Python in favor of efficient compiled languages. Languages such as Fortran and C++, Zwart calculates, are more than 100 times more carbon efficient than Python because they require fewer operations. Another option, says MPIA’s Knud Jahnke, is to set up supercomputers in Iceland, with its carbon-free geothermal power and cold climate, which reduces cooling needs, or in other countries with plentiful renewable energy.

Major observatories are also taking action. ESO completed a solar power array in 2016 for its La Silla Observatory in Chile and last year inked a deal for a photovoltaic plant to help cool its Extremely Large Telescope, now under construction near Paranal. The Keck and Gemini telescopes in Hawaii and the Murchison Radio-astronomy Observatory in Australia have installed solar arrays, too. To cut down on flying, more and more telescopes are making remote observing routine. Max says the University of California built remote observing rooms on its far-flung campuses so researchers didn’t need to travel to Lick and other telescopes. Since the arrival of COVID-19, the scheme has been extended to home laptops—“pajama observing,” Max calls it. “The days of flying to Hawaii to observe are numbered,” she says.

Meetings are another target ripe for reform. “There’s a lot of excitement about the potential” of virtual meetings, says Travis Rector of the University of Alaska, Anchorage, who heads the sustainability committee of the American Astronomical Society (AAS). When this year’s EAS meeting went virtual because of COVID-19, the team that calculated the carbon costs of the 2019 meeting did a new analysis. Based on a survey of computer and internet usage by delegates and organizers, they calculated emissions of 582 kilograms for the entire meeting, less than one–three-thousandth of the 2019 meeting total. “That really gave a pause for thought,” says Mark McCaughrean, an author and a senior adviser at the European Space Agency.

EAS is studying a hybrid format for future meetings, where those farther away would take part virtually. Rector says AAS has contracts that commit it to several years of in-person meetings, but he expects the society to move to virtual meetings after that. Societies, he says, “will learn from each other how to do it better.”

This month, Lick workers cleared brush and trees around the site to lessen the risk of future fires. Astronomers need to take action, too, Burtscher says. It’s a moral decision—and a practical one, he says. “We need to change in order to continue our professions.”