Rising CO2 and a Cooling Upper Atmosphere: Why Space Communications Could Be at Risk
As global warming accelerates, researchers are turning their attention to how atmospheric changes affect the ionosphere, a region roughly 60 to 1,000 kilometers above Earth. A team from Kyushu University has found that higher carbon dioxide (CO2) levels, while warming Earth’s surface, are cooling the upper atmosphere. This cooling alters wind patterns and air density at altitudes where radio waves travel, with potential consequences for shortwave communications used in air traffic control, maritime operations, and broadcasting.
What happens in the ionosphere?
The ionosphere is a charged layer formed by solar radiation striking the upper atmosphere. It plays a crucial role in reflecting and guiding radio waves, especially at high frequencies. In this study, researchers focused on a lesser-known feature called sporadic-E, or Es, a dense, transient layer of metal ions that forms between 90 and 120 kilometers above the surface.
Es is notable for its unpredictability. When it occurs, it can disrupt high-frequency (HF) and very-high-frequency (VHF) radio communications by altering how radio waves propagate. The Kyushu University team, led by Professor Huixin Liu, used a whole-atmosphere model to simulate conditions under two CO2 scenarios: a baseline atmosphere near 315 ppm and a higher CO2 case at about 667 ppm, reflecting future projections beyond 2024 levels.
Key findings: how CO2 affects Es and radio signals
Two main trends emerged from the simulations: first, vertical ion convergence (VIC), the process that concentrates charged particles to form Es, becomes stronger at 100–120 km under higher CO2. Second, the Es hotspots shift downward by roughly 5 kilometers and show longer persistence at night. The result is a louder, longer-lasting Es presence in the portion of the ionosphere most relevant to shortwave and VHF radio.
These changes are driven by a cooler, rarer upper atmosphere that reduces air density and disturbs wind patterns. In practice, stronger Es at lower altitudes, combined with altered diurnal behavior, can degrade the reliability of radio links used by aircraft and ships, as well as certain broadcasting services that rely on ionospheric reflection.
Why this matters for space and earth-based communications
The implications extend beyond immediate signal quality. Es influences not only radio communications but also satellite tracking and the orbiting lifetime of space debris and satellites through changes in atmospheric drag and plasma interactions. The researchers emphasize that the interplay between neutral air dynamics and ionospheric plasma—what they call cross-scale coupling—means climate-driven shifts at Earth’s surface can ripple into space weather phenomena.
“These findings are the first of their kind to show how increasing CO2 affects the occurrence of Es,” said Liu. “They reveal new insights into cross-scale coupling processes between neutral air and ionosphere plasma.” The study, published in Geophysical Research Letters, underscores the complexity of forecasting space weather and the need to integrate climate models with ionospheric physics.
What scientists and policymakers should consider
As CO2 levels rise, telecom and aviation industries may need to adapt by diversifying communication paths, investing in more robust HF/VHF systems, or improving satellite and ground-based monitoring of Es activity. The Kyushu University work highlights a critical area where climate change can indirectly impact daily life, from navigation safety to broadcast reliability, even as surface temperature trends dominate public discourse.
Future research will likely examine regional variability in Es response to CO2 and explore mitigation strategies for critical communication facilities. By deepening our understanding of how global climate shifts influence ionospheric processes, scientists can help ensure resilient space and earth-based communication networks in a warming world.
