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

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Title: Variability and Trends in Cloud Properties Over 17 Years From CALIPSO Space Lidar Observations.
Authors: Chepfer, H.1 (AUTHOR) chepfer@lmd.polytechnique.fr, Chomette, O.1 (AUTHOR), Arouf, A.2 (AUTHOR), Noel, V.3 (AUTHOR), Winker, D.4 (AUTHOR), Feofilov, A.1 (AUTHOR), Alava Baldazo, A.1 (AUTHOR)
Source: Journal of Geophysical Research. Atmospheres. 10/28/2025, Vol. 130 Issue 20, p1-20. 20p.
Subject Terms: *Climate change, Cloudiness, Atmospheric models, Ceilometer, Atmospheric physics, LIDAR, Statistics
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. Plain Language Summary: How clouds are changing under the influence of human‐induced climate warming is not yet established because the forced changes are small compared to natural variability, although this has important impacts on the amplitude of the surface temperature increase and on the change in precipitation distribution and intensity. We searched fingerprints of cloud changes into observations collected during the last 17 years by a laser on board a satellite because these observations are well suited for that purpose. They are global, less sensitive to calibration errors than usual passive remote sensing satellites, almost insensitive to the surface type (ocean, continent, ice) and they document more precisely than other satellites variations in the vertical distribution of clouds. We found some observed signatures of changes in line with climate model projections such as an increase in cloud altitude and a decrease in the cover of opaque clouds, but none of the observed changes are robust statistically. As a consequence, if the observational results presented in the current paper do not validate the model‐based projected cloud change, they can neither reject them at that stage. A new space lidar launched in 2024 is currently collecting data to extend the observed record; it will perhaps allow us to observe reliable cloud changes. Key Points: As the climate warms, space lidars are well suited to observe the predicted cloud changesThe 17 years space lidar record reduced to 11 years after removing artifacts and limitation based on instrument operationAnalysis of seasonal anomalies show no statistically significant trends in cloud properties [ABSTRACT FROM AUTHOR]
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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. Plain Language Summary: How clouds are changing under the influence of human‐induced climate warming is not yet established because the forced changes are small compared to natural variability, although this has important impacts on the amplitude of the surface temperature increase and on the change in precipitation distribution and intensity. We searched fingerprints of cloud changes into observations collected during the last 17 years by a laser on board a satellite because these observations are well suited for that purpose. They are global, less sensitive to calibration errors than usual passive remote sensing satellites, almost insensitive to the surface type (ocean, continent, ice) and they document more precisely than other satellites variations in the vertical distribution of clouds. We found some observed signatures of changes in line with climate model projections such as an increase in cloud altitude and a decrease in the cover of opaque clouds, but none of the observed changes are robust statistically. As a consequence, if the observational results presented in the current paper do not validate the model‐based projected cloud change, they can neither reject them at that stage. A new space lidar launched in 2024 is currently collecting data to extend the observed record; it will perhaps allow us to observe reliable cloud changes. Key Points: As the climate warms, space lidars are well suited to observe the predicted cloud changesThe 17 years space lidar record reduced to 11 years after removing artifacts and limitation based on instrument operationAnalysis of seasonal anomalies show no statistically significant trends in cloud properties [ABSTRACT FROM AUTHOR]
ISSN:2169897X
DOI:10.1029/2025JD043764