Rising CO2 Is Changing the Sky: Stronger, Lower Sporadic‑E Layers Could Disrupt Radio and Satellites

Rising CO2 Is Altering the Upper Atmosphere — and Our Radios

Far above where aircraft fly and people live, carbon dioxide is already changing the upper atmosphere in ways that could affect radio and satellite systems. A new modeling study by researchers at Kyushu University and Japan’s National Institute of Information and Communications Technology (NICT), published in Geophysical Research Letters, shows that rising CO2 can strengthen and lower sporadic‑E (Es) layers in the ionosphere’s metal‑rich E region.

What is the sporadic‑E layer?

The E region sits roughly 60–75 miles above Earth (about 100–120 km) and contains a thin cloud of metallic ions created when meteors ablate — depositing iron, magnesium and calcium into the atmosphere. Under certain conditions these ions can collect into a paper‑thin band called the sporadic‑E layer (Es). Although only a few miles thick, Es layers can stretch horizontally for hundreds of miles and act like natural mirrors that reflect radio waves back to the ground.

That mirror effect can be useful for long‑distance HF and VHF communications used by pilots, ship crews and emergency services, but Es can also bend, scatter or block navigation and voice signals and degrade reception. Es layers are unpredictable: they can appear suddenly, persist for an hour or more, then vanish without warning. Professor Huixin Liu of Kyushu University, who leads this work, notes:

“Es are sporadic, as the name indicates, and are unpredictable. But when they occur, they can disrupt HF and VHF radio communications.”

How CO2 changes Es

Using the whole‑atmosphere GAIA model, Liu and colleagues simulated a scenario in which atmospheric CO2 doubles from pre‑industrial levels (315 ppm) to 667 ppm — a level some projections place near 2100. (For context, the global average in 2024 was about 423 ppm.) The team ran the model for summertime conditions, when Es activity is most lively, and focused on vertical ion convergence (VIC), the process by which metallic ions converge vertically to form and sustain Es layers. Higher VIC generally produces thicker, longer‑lasting Es.

The simulations show that when CO2 is doubled, VIC increases globally at altitudes near 100–120 km. Metallic "hotspots" where ions cluster shift downward by roughly 5 km, bringing Es formation closer to lower altitudes. The Es layers also become thicker and last longer, especially overnight — changes that could make their effects on communications more persistent.

Why does more CO2 cool the upper atmosphere?

It may seem counterintuitive that adding CO2 cools the very high atmosphere while warming Earth’s surface, but the physics are well understood. Near the surface CO2 acts as a greenhouse gas and traps heat. High above, in very thin air, CO2 radiates heat efficiently to space. As the thermosphere cools, air density drops and collisions between metallic ions and neutral particles decline. Liu explains:

“With fewer collisions, metallic ions move more freely. That enables them to build up into stronger and denser layers.”

Temperature changes also modify high‑altitude tidal winds that sweep east–west like invisible combs, collecting ions into bands. Increased CO2 alters those wind patterns and shifts convergence zones, reinforcing stronger and deeper Es layers.

Observed and practical impacts

The research team tested the model at two geomagnetically different sites — Kokubujin, Japan, and the Arecibo area near Puerto Rico — and found the same overall trend. In Japan, Es activity that previously peaked during daylight began to persist into night in the high‑CO2 scenario. In Puerto Rico, layers grew denser and appeared at lower altitudes. The authors suggest similar enhancements could emerge in many other regions as global emissions rise.

For pilots, radio operators and space agencies, these changes matter. Stronger, lower sporadic‑E layers can deform or unpredictably reflect radio waves, interfering with HF/VHF signals used by aviation, military radar and maritime communications. Liu cautions:

“This cooling does not necessarily mean all is good. It shrinks the air density in the ionosphere and strengthens the wind circulation. This can also change the orbit and lifetime of satellites and space debris and disrupt radio communications from localized small‑scale plasma irregularities.”

Next steps and broader implications

The researchers plan to refine their results by combining GAIA simulations with satellite observations and ground radar data, and by studying local chemistry and gravity waves that modulate metallic layers. Improved forecasts for sporadic‑E events could help aviation, maritime and telecommunications planners adapt—for example, by adjusting routing, frequency allocations or satellite design to be more resilient.

As Liu summarizes, “Global warming doesn’t stop at the ground — it reaches well into space.” Understanding how CO2 reshapes the ionosphere will be important for protecting communication and satellite systems on which modern life increasingly depends.

Reference: Liu et al., Geophysical Research Letters. Model results and data are available in the published paper.