New research conducted by scientists at Lawrence Livermore National Laboratory (LLNL) has revealed that human activities are significantly altering the thermal structure of Earth’s atmosphere. By expanding climate “fingerprinting” techniques to the mid-to-upper stratosphere, the team has improved the detection of human effects on the climate by a factor of five. The distinct patterns of CO2-driven temperature changes in these areas highlight that natural causes cannot explain these shifts.
The analysis conducted by LLNL scientists shows that it is now virtually impossible for natural causes to account for the observed changes in the thermal structure of Earth’s atmosphere as measured by satellites. By extending fingerprinting techniques to the upper stratosphere (25-50 kilometres above the surface), the researchers have obtained clear evidence of human effects on the thermal structure of the atmosphere. This approach considers the differences between temperature trends in the lower layer of the atmosphere (troposphere) and the lower stratosphere, which have long been recognized as a fingerprint of human-induced climate change. However, previous studies neglected information from the mid-to-upper stratosphere.
The team compared improved climate model results with observed temperature measurements over 37 years and found that natural causes cannot explain the measured trends in the full structure of Earth’s atmosphere. The signal of human-caused climate change becomes more easily distinguishable in the upper stratosphere, where the noise of variability is smaller and the human-induced climate change signal is larger.
The distinctive pattern and magnitude of stratospheric temperature change due to CO2 emissions contribute to its detectability. Human-induced stratospheric cooling, which increases with altitude, is much larger compared to natural variations in stratospheric temperature, resulting in a distinct cooling pattern. The predictions made by early climate models, such as the cooling of the stratosphere due to CO2 emissions, have been confirmed by more complex models and observations.
This research highlights the undeniable influence of human activities on Earth’s atmosphere and provides further evidence of the need to address climate change through mitigation and adaptation efforts.