Rising Carbon Dioxide Levels Raise Concerns Over Cooling in Earth’s Upper Atmosphere

While increasing carbon emissions are heating Earth’s atmosphere near the planet’s surface, higher carbon dioxide levels are cooling the upper atmosphere. Scientists say this phenomenon could impact satellites and the ozone layer, and contribute to weather changes below.

A new study published in PNAS adds to the evidence of humanity’s fingerprint on climate change. While previous studies have tracked changes in the troposphere (where nearly all Earth’s weather happens) and lower stratosphere, the study noted that there was information lacking for the region 30 to 50 kilometers (approximately 18.6 to 31.1 miles) from Earth’s surface, or the mid to upper stratosphere.

Researchers finding temperature changes in the upper atmosphere means that humanity’s impact on climate is now five times more detectable. According to the study, is is now “virtually impossible for natural causes to explain satellite-measured trends in the thermal structure of the Earth’s atmosphere.”

The cooling trends in the upper atmosphere raise new concerns. The stratosphere and other outer layers of the atmosphere, like the mesosphere and the thermosphere, each have unique and harsh environments, with high winds and air that can quickly rise and fall within and beyond each layer. The concern now is that increasing carbon dioxide emissions can alter these patterns.

“This research undercuts and rebuts claims that recent atmospheric and surface temperature changes are natural, whether due to the Sun or due to internal cycles in the climate system. A natural explanation is virtually impossible in terms of what we are looking at here: changes in the temperature structure of the atmosphere,” Benjamin Santer, lead author of the study and adjunct scientist in the Physical Oceanography Department at the Woods Hole Oceanographic Institute (WHOI) in Massachusetts, said in a statement. “This research puts to rest incorrect claims that we don’t need to treat climate change seriously because it is all natural.”

From 2002 to 2019, the mesosphere and lower thermosphere experienced 1.7°C of cooling, as reported by Yale Environment 360. With carbon dioxide levels expected to double later this century, cooling in the upper atmosphere could reach 7.5°C.

Further, a 2022 study found that these same areas shrunk 1,333 meters (about 4,373 feet) from 2002 to 2019, with 342 meters (1,122 feet) of shrinkage attributed to higher carbon dioxide levels. The stratosphere has also contracted, and one study predicted shrinkage in this part of the atmosphere could reach 1.3 kilometers (0.81 miles) by 2080.

These changes can allow space waste to remain in the atmosphere for longer and could inhibit the ozone layer’s healing, which was previously expected to recover by 2040. They could also lead to more frequent, sudden and intense weather changes closer to Earth’s surface.

“As someone who tries to understand the kind of world that future generations are going to inhabit, these results make me very worried. We are fundamentally changing the thermal structure of Earth’s atmosphere, and there is no joy in recognizing that,” Santer said.

“We now face important decisions, in the United States and globally, on what to do about climate change,” Santer added. “I hope those decisions are based on our best scientific understanding of the reality and seriousness of human effects on climate.”