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The ocean takes up about 93% of the global warming heat entering Earth’s climate system. In addition, the associated thermal expansion contributes substantially to sea-level rise. Hence, quantifying the oceanic heat uptake rate and its statistical significance has been a research focus. Here we use gridded ocean heat content maps to examine regional trends in ocean warming for 0–700 m depth from 1993–2019 and 1968–2019, periods based on sampling distributions. The maps are from four research groups, three based on ocean temperature alone and one combining ocean temperature with satellite altimeter sea-level anomalies. We show that use of longer periods results in larger percentages of ocean area with statistically significant warming trends and less ocean area covered by statistically significant cooling trends. We discuss relations of these patterns to climate phenomena, including the Pacific Decadal Oscillation, the Atlantic Meridional Overturning Circulation and global warming. A large proportion of anthropogenic heat energy is being taken up by ocean warming. Analysis of yearly 0–700 m ocean heat content maps from four different estimates shows that the longer the period over which regional trends are estimated, the larger the area of statistically significant warming.

Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by the Earth and the thermal radiation emitted back to space. A revised analysis of measured changes in the net radiation imbalance at the top of the atmosphere, and the ocean heat content to a depth of 1,800 m, suggests that these two sets of observations are consistent within error margins.

The relative significance of short multi-year linear trends in the global integral of 0–700 m ocean heat content anomaly (OHCA) is investigated by examining the overlapping segments of the 16-year OHCA curve from Lyman et al. (Nature 465:334–337, 2010). Segments of 4 years and less are found not to be significantly different from each other or from 0 at the 90% confidence interval. Likewise, short 5- to 7-year segments are not statistically different from each other. Ten-year and longer trends are significant and provide a useful comparison for satellite observations of the radiation imbalance at the top of the atmosphere.

In recent decades, over nine-tenths of Earth's top-of-the-atmosphere energy imbalance has been stored in the ocean, which is rising as it warms. Combining satellite sea-level data with ocean mass data or model results allows insights into ocean warming.