Study provides more evidence of climate change being human-caused: PNAS

A new research has provided evidence of climate change being human-caused and showed that specific signals from human activities have altered the temperature structure of Earth's atmosphere.

Scientists have long recognised differences between tropospheric and lower stratospheric temperature trends as a "fingerprint" of human effects on climate.

This fingerprint, however, neglected information from the mid to upper stratosphere, 25 to 50 kilometres above the Earth's surface, the inclusion of which improves the detectability of a human fingerprint by a factor of five, the scientists involved in the study said.

"Enhanced detectability occurs because the mid to upper stratosphere has a large cooling signal from human-caused CO2 increases, small noise levels of natural internal variability, and differing signal and noise patterns," the study published in Proceedings of the National Academy of Sciences (PNAS) said.

Noise in the troposphere can include day-to-day weather, interannual variability arising from El Nios and La Nias, and longer-term natural fluctuations in climate. In the upper stratosphere, the noise of variability is smaller, and the human-caused climate change signal is larger, so the signal can be much more easily distinguished.

"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," the paper stated.

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

"This research puts to rest incorrect claims that we don't need to treat climate change seriously because it is all natural," said Santer, who has worked on climate fingerprinting for more than 30 years.

This layer, from the mid to upper stratosphere, which the earlier studies had not studied in detail, can now be studied better because of improved simulations and satellite data. The new research is the first to search for human-caused climate change patterns in the middle and upper stratosphere, the scientists said.

"These unique fingerprints make it possible to detect the human impact on climate change due to CO2 in a short period of time (10 15 years) with high confidence," stated co-author Qiang Fu, a professor in the Department of Atmospheric Sciences at the University of Washington, US.

"The world has been reeling under climate change, so being as confident as possible of the role of carbon dioxide is critical," said co-author Susan Solomon, Martin Professor of Environmental Studies at the Massachusetts Institute of Technology.

"The fact that observations show not only a warming troposphere but also a strongly cooling upper stratosphere is unique tell-tale evidence that nails the dominant role of carbon dioxide in climate change and greatly increases confidence," said Solomon.

"This study shows that the real world has changed in a way that simply cannot be explained by natural causes," Santer said.