In the early hours of 1 July, an outdoor emergency alarm sounded in Huntington County, Indiana, despite no storm, tornado, or other emergency weather event within hundreds of miles. Thomas Fuller, the county's deputy director for emergency management, said the siren activated due to radio signals originating from Iowa, 300 miles away. The incident occurred amid a heat dome weather event that affected millions across the Midwest and East Coast.
Tropospheric Ducting Explained
These disruptions are caused by tropospheric ducting, a phenomenon where high temperatures create atmospheric tunnels that allow radio, television, and microwave signals to travel far beyond their normal range. Kyle Spillane, a member of the Mid-MO Amateur Radio Club, described it as "little tunnels in the sky that the radio waves bounce through until they eventually come out." Key factors include temperature, air pressure, and humidity.
In Ohio, drivers reported their car radios suddenly picking up stations hundreds of miles away or losing coverage entirely. Tropospheric ducting can last from minutes to hours, depending on weather conditions.
Impact on Emergency Communications
Radio remains critical during emergencies when internet and cell service fail. Forest firefighters, railroad workers, and maritime industries around the Great Lakes rely on it. A 2023 study found that the Pacific Northwest, where radio is vital for forestry and emergency responders, is expected to experience more "heat-dome-like circulation," with human-caused climate change increasing the probability of extreme heatwaves by at least 150 times. The 2021 heat dome in that region caused an estimated 1,200 deaths in Washington, Oregon, and British Columbia.
Tropospheric ducting can also affect radar, pacemakers, internet routers, satellites, and cell phones—especially 5G devices, which use higher frequencies. Spillane noted, "Your cellphone is a radio; it just operates on a higher frequency, and the higher the frequency, the more likely it is to be affected."
False Alarms and Alert Fatigue
Fuller expressed concern that false alarms could lead to "alert fatigue," where the public becomes desensitized to warnings. A series of false alarms at a Washington state dam community forced alarms to be turned off. "It’s happened a couple of times, three or four years ago, where we get these signals from different places," Fuller said. Despite these incidents, some agencies report minimal impact. A US Forest Service spokesperson stated that their firefighters experience little to no radio disruption due to heat, though they did not comment on tropospheric ducting links.
For amateur radio enthusiasts, tropospheric ducting can be a boon, allowing communication over hundreds of miles with inexpensive equipment. Spillane acknowledged it as "another aspect of climate change that people need to consider," but emphasized more pressing climate concerns.
