Here is a second collection of plots showing time series of surface observed total cloud cover, low-level cloud cover, and upper-level (combined mid+high) cloud cover globally averaged over land only during 1971-1996, ocean only during 1952-1997, and land+ocean during 1971-1996. I also show the spatial pattern of correlation of each local grid box time series with the global time series. The quick summary is that the correlation patterns are generally uniform over land and over ocean, with increasing trends in total cloud cover and low-level cloud cover over ocean and decreasing trends in total cloud cover and low-level cloud cover over land.

Looking at the land-only total cloud time series, it appears that total cloud cover during the 1970s was greater than cloud cover during the 1980s and 1990s. The correlation map indicates that southwest Asia, Africa, Central America, and South America contribute most strongly to the global land trend. Contrastingly, the ocean-only total cloud time series exhibits increasing cloud cover since 1952 and especially after 1980. Almost all areas of the ocean have a weak positive correlation with the global ocean time series, and correlation values are slightly higher in the North Atlantic. The land+ocean total cloud time series is dominated by the ocean given its greater area and exhibits an increasing cloud trend between 1971 and 1996.Most ocean areas are positively correlated with the land+ocean global mean time series, and negative correlations are seen over South America, southern Africa, and China, presumably because these land regions have decreasing total cloud cover.

The ocean-only global mean low-level cloud time series exhibits a strongly increasing trend prior to ~1970 and after ~1990, suggesting that it is the trend in low-level cloud amount that is driving the total cloud cover trend. Positive correlations occur almost everywhere in the ocean-only correlation map and are especially strong in the western North Atlantic and midlatitude North Pacific. Contrastingly, a slight decreasing trend occurs in the land-only global mean time series, with positive correlations over most land areas. The ocean time series dominates in the land+ocean global mean time series, which is flat from 1971 to ~1990 and strongly increase thereafter. The land+ocean correlation map exhibits positive correlations over almost all ocean grid boxes and negative correlations over many land grid boxes, consistent with the generally increasing trend in low-level cloud over ocean and decreasing trend over land.

The upper-level cloud time series for ocean-only, land-only, and land+ocean global averages exhibit substantial interdecadal variability on top of a generally decreasing trend over land and ocean. The ocean-only correlation map shows weak positive correlations almost everywhere, and the land-only correlation map shows positive correlations over South America, Africa, and Asia. In the land+ocean correlation map, weak positive correlations prevail, especially over the ocean but also over many areas of land.