UCLA published a press release on a research recently published in PNAS led by JIFRESSE Researcher Ben Santer. This represents the first study to search for human-caused climate patterns in the middle and upper stratosphere. According to the study, cooling in the middle and upper stratosphere is a consequence of human-caused increases in greenhouse gases, which cause heat to be retained more effectively in the troposphere, the lowest level of the atmosphere. 

Please see more details from the UCLA press release: https://newsroom.ucla.edu/releases/stratospheric-cooling-vertical-fingerprinting.

A link to the PNAS paper can be found here: https://www.pnas.org/doi/10.1073/pnas.2300758120.