A recent study published in Proceedings of the National Academy of Sciences (PNAS) has provided stronger evidence of human-caused climate change fingerprints in Earth’s atmosphere. The research, conducted by a team of scientists led by Benjamin Santer, an adjunct scientist in the Physical Oceanography Department at the Woods Hole Oceanographic Institute (WHOI) in Massachusetts, US, has shown that specific signals from human activities have altered the temperature structure of Earth’s atmosphere.
The study’s authors have long recognised differences between tropospheric and lower stratospheric temperature trends as a “fingerprint” of human effects on climate. However, they have found that this fingerprint neglected information from the mid to upper stratosphere, 25 to 50 kilometres above the Earth’s surface, which can improve the detectability of a human fingerprint by a factor of five.
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. 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. This makes it now virtually impossible for natural causes to explain satellite-measured trends in the thermal structure of the Earth’s atmosphere.
The new research is the first to search for human-caused climate change patterns in the middle and upper stratosphere. By including data from this layer, which the earlier studies had not studied in detail, and by using improved simulations and satellite data, it is now possible to detect the human impact on climate change due to CO2 in a short period of time (10-15 years) with high confidence.
The study’s findings have put to rest incorrect claims that climate change is all natural and that there is no need to treat it seriously. The scientists hope that this research will increase confidence in the role of carbon dioxide in climate change and will encourage policymakers to take more aggressive measures to reduce carbon emissions.