Independent lidar observations support declining low cloud cover trends seen in satellite and reanalysis records

Sasu Karttunen, Stephan R. de Roode, Angela Meyer

Low clouds strongly influence Earth's radiation budget, yet their response to climate change remains uncertain. Recent satellite and reanalysis studies indicate declining low cloud cover that may have contributed to increasing absorbed solar radiation, but independent ground-based evidence over land is limited. Here we show that ground-based lidar observations support a decrease in low cloud cover across mid- to high-latitude land regions. We analyse harmonised 10–25-year records from 16 sites and compare their trends with collocated satellite and reanalysis estimates. Daytime joint trends are significantly negative at the 5% level across datasets, despite considerable variability among sites. Trends are negative at 12–14 of 16 sites across datasets, although their magnitudes differ substantially. Nighttime trends show greater cross-site and cross-dataset variability. Overall, independent lidar observations support the general tendency toward declining low cloud cover indicated by satellite and reanalysis records.