A remarkable interagency battle is playing out within the U.S. government over whether plans for the next generation of wireless technology, known as 5G, will threaten accurate weather forecasts—and, if so, how to mitigate the threat. Months of technical studies and debate have only deepened the impasse.
NASA and the National Oceanic and Atmospheric Administration (NOAA) say 5G antennas will blast signals near the frequencies their satellites use to gather critical water vapor data, and could compromise forecasts and science. The agencies are calling for tight limits on stray noise. The Federal Communications Commission (FCC), which licenses the wireless spectrum for 5G operators in the United States, says those fears are overblown.
Jordan Gerth, a meteorologist at the University of Wisconsin in Madison, says 5G poses "a clear threat" to weather forecasting, but adds that "the devil is in the details." Attempts to reach a compromise have faltered, and a July workshop organized by the National Academies of Sciences, Engineering, and Medicine to search for a solution was canceled when federal agencies declined to attend. A series of international meetings beginning next week aims to hammer out global 5G regulations—but forecasters fear U.S. delegates will not argue for strict limits.
5G promises data speeds up to 100 times faster than current 4G networks; it could pave the way for widespread adoption of cutting-edge technologies such as autonomous cars. Already, telecom companies have begun to attach suitcase-size 5G antennas to cellphone towers and rooftops in cities around the world.
The companies want to expand service into additional frequency bands such as one at 24 gigahertz (GHz)—a frequency much higher than those used by existing wireless networks—because they can pack more information into the signals, and because the atmosphere is transparent to signals in the band. But such frequency bands are useful only if companies can blast data at relatively high signal strengths. FCC has proposed allowing noise as high as −20 decibel watts (dBW) in all bands auctioned off so far, including one between 24.25 and 25.25 GHz.
But a nearby frequency is critical for weather forecasters. At about 23.8 GHz, water vapor molecules emit a small amount of radiation—one of the best ways to remotely sense the atmospheric water content that fuels clouds and storms. Because air is transparent at those frequencies, sensors attached to NOAA's Joint Polar Satellite System and the European Meteorological Operational satellites can collect data from all levels of the atmosphere, providing a crucial input not just for familiar 7-day weather forecasts, but also for predicting the strength of hurricanes and where they will make landfall. A long-term water vapor record can also help calibrate climate change models, adds Eric Allaix, a meteorologist at Météo-France in Toulouse who leads a World Meteorological Organization committee on radio frequency coordination.
Even though 5G transmissions will be separated from the water vapor band by a 250-megahertz (MHz) buffer, forecasters worry they will bleed into the band and swamp the faint natural emission. In March, just before FCC's auction of 24-GHz band frequencies, Secretary of Commerce Wilbur Ross, who oversees NOAA, and NASA Administrator Jim Bridenstine sent a letter asking FCC to postpone the auction. FCC went ahead with it anyway, and both T-Mobile and AT&T bought parts of the band.
Things heated up from there. Neil Jacobs, NOAA's acting administrator, testified to Congress in May that an internal study had found 5G-related interference could cost NOAA 77% of the water vapor data it collects at 23.8 GHz, and could degrade weather forecasts by up to 30%, to 1980 levels. "It's a critical data set for us," Jacobs said. Bridenstine has echoed Jacobs's concerns, and the Navy also worries about deteriorating forecast quality.
NOAA misunderstands 5G technology, FCC Chairman Ajit Pai said in his own congressional testimony in June. 5G will use laserlike "beam-forming" technology, which will maximize data transmission rates and minimize stray signals, Pai said. And the 24-GHz band will probably be limited to dense urban areas with many mobile phone users, justifying companies' investments in the transmitter networks.
But Gerth fears that even if focused in beams and corralled to cities, 5G signals could still cause problems. Weather satellites see many square kilometers at once, and interference in part of a pixel could ruin the entire pixel, he says. Moreover, interference in coastal cities such as New York City and Miami, Florida, could hamper oceanic observations crucial to hurricane prediction.
Since April, NOAA and NASA have refined their study of the effect of 5G on their forecasts, in response to critiques from FCC and the wireless industry. According to sources who have seen the latest versions of the study, the agencies reach the same conclusion: Noise needs to be limited to about −42 dBW to protect weather data. (Because dBW is a logarithmic unit, this represents a limit more than 100 times stricter than FCC's.) "The studies appear to validate all the public claims from NASA and NOAA," says a staff member of a House of Representatives committee who has reviewed them.
But NOAA has not released the studies publicly or submitted them to FCC—the result, suggest some congressional sources, of pressure from the White House, which has strongly backed 5G. "The chairman has said we're happy to look at studies," says Brian Hart, an FCC spokesperson in Washington, D.C. "No verifiable studies have been presented." (Neither NASA nor NOAA would comment to Science.)
Even if technical experts cannot resolve their disputes, diplomats might. At a meeting hosted by the Inter-American Telecommunication Commission, which will take place next week in Ottawa, Western Hemisphere nations will try to come to a consensus on 5G limits. They will bring that number to the quadrennial World Radiocommunication Conference, which will start on 28 October in Sharm El-Sheikh, Egypt, in an effort to negotiate a global limit. The Department of State will lead the U.S. delegation, but has not yet announced its position.
Jacobs briefed congressional staff 2 weeks ago. According to sources, he reported that an interagency compromise-seeking process had broken down and hinted that the United States may advance a noise limit of −28 dBW in Ottawa. That is more stringent than the −20 dBW that FCC has pushed for, but Jacobs reportedly believes it is still potentially disastrous for weather forecasting.
Europe may provide a precautionary counterweight. The regional telecommunication organization representing European countries plans to propose a −42-dBW limit at the radiocommunication conference, says Allaix, who co-authored a 2018 study that supports such a limit. The World Meteorological Organization has taken an even harder line, calling for −55 dBW. U.S. atmospheric conditions are critical for European forecasts 2 to 3 days later, so it "is really a worldwide issue," Allaix says. "Our satellites need to be protected everywhere around the world."
Resolving the battle over the 24-GHz band won't end the war. In December, FCC plans to auction off frequencies in the 37.6- to 38.6-GHz band, close to those used to measure rain and snow. And several other potential 5G bands sit near weather-critical frequencies. Gerth is especially worried about frequencies between 50 and 55 GHz, necessary for atmospheric temperature profiles. "It's an issue that's not going to go away," he says.
*Correction, 14 August, 2:35 p.m.: An earlier version of the story mistakenly described 5G noise limits as limits to the signal strength itself.