Variability and Trends in Cloud Properties Over 17 Years From CALIPSO Space Lidar Observations

Abstract In this paper we search for fingerprints of cloud changes over 17 years (2006–2023) within the record of cloud properties collected by the CALIPSO space lidar. Indeed, climate model projections suggest that clouds are rising up in altitude, shrinking in cover and changing rapidly in the Arctic under the influence of human induced climate warming. We describe how changes in CALIPSO space lidar operations over the mission have impacted the stability of the cloud detection. Removing contaminated data reduces the record to 11 full years (2008–2018). For these 11 years, we analyze de‐seasonalized anomalies of cloud cover, altitude, emissivity and vertical profile, to identify trends at global scale and in specific latitude bands. Results show a decrease in opaque cloud cover and a rise in opaque cloud altitude, consistent in sign with climate model projected changes, but statistically insignificant in the observations. Observed changes do not extend beyond the natural variability in any statistically significant way. This suggests that if cloud changes exist, the CALIPSO record might be too short in time or not precise enough to detect them with confidence. This study underscores the need for extending the cloud record from space lidars and building a harmonized record from observations made by successive space lidars.