CO2 Increases Linked to Human-Induced Climate Change, Supported by Atmospheric Research Findings

New research has shown that certain signals from human activities have altered the temperature structure of Earth’s atmosphere, which provides clear evidence of a human “fingerprint” on climate change. Differences between tropospheric and lower stratospheric temperature trends have been widely recognized as a fingerprint of human effects on climate; however, this neglected the mid to upper stratosphere which is 25 to 50 kilometers above Earth’s surface. The journal article, “Exceptional stratospheric contribution to human fingerprints on atmospheric temperature,” published in the Proceedings of the National Academy of Sciences (PNAS) pointed out that including information from this region improves the detectability of a human fingerprint by five times because of the large cooling signal from human-caused CO₂ increases. Noise in the troposphere comes from day-to-day weather, interannual variability, and longer-term fluctuations, while the noise of variability is smaller in the upper stratosphere and the human-caused climate change signal is larger. This makes it more easily distinguished.

The paper stated, “Extending fingerprinting to the upper stratosphere with long temperature records and improved climate models means that it is now virtually impossible for natural causes to explain satellite-measured trends in the thermal structure of the Earth’s atmosphere.”

Lead author Benjamin Santer, an adjunct scientist in the Physical Oceanography Department at the Woods Hole Oceanographic Institute (WHOI) in Massachusetts, said, “This is the clearest evidence there is of a human-caused climate change signal associated with CO₂ increases.”

The study undercuts and refutes claims that recent atmospheric and surface temperature changes are natural phenomenon. The research was motivated by the work in 1967 by Suki Manabe and Richard Wetherald, who used a simple climate model to show how CO₂ from fossil fuel burning might change atmospheric temperature.

The new research is the first to search for human-caused climate change patterns in the middle and upper stratosphere.

The previous studies from 1967 considered global-mean temperature changes in the middle and upper stratosphere, but did not look at detailed patterns of climate change in this layer. The new research is unique and provides a new clarity to the study of human impact on climate change.

Co-author Qiang Fu, a professor at the Department of Atmospheric Sciences at the University of Washington, stated, “The human fingerprints in temperature changes in the mid to upper stratosphere due to CO₂ increase are truly exceptional because they are so large and so different from temperature changes there due to internal variability and natural external forcing. These unique fingerprints make it possible to detect the human impact on climate change due to CO₂ with high confidence in a short period of time (~10-15 years).”

Co-author Susan Solomon, Martin Professor of Environmental Studies at the Massachusetts Institute of Technology, added that the unique tell-tale evidence proves the dominant role of carbon dioxide in climate change and increases confidence.

The study reveals that the real world has changed in a way that cannot be explained by natural causes. Santer noted, “we are fundamentally changing the thermal structure of Earth’s atmosphere, and there is no joy in recognizing that.”