As this article points out, "Water is a more appropriate metric for heat accumulation than air because of its ability to store heat. For this reason, it is also a more robust metric for assessing global warming and cooling...
For any given area on the ocean’s surface, the upper 2.6m of water has the same heat capacity as the entire atmosphere above it! Considering the enormous depth and global surface area of the ocean (70.5%), it is apparent that its heat capacity is greater than the atmosphere by many orders of magnitude. Consequently... the ocean must be regarded as the main reservoir of atmospheric heat and the primary driver of climate fluctuations.
Heat accumulating in the climate system can be determined by profiling ocean temperature... These measurements are now possible on a global scale with the ARGO buoy array and from satellite measurements of ocean surface heights. ARGO consists of a world-wide network of over 3000 free-drifting platforms that measure temperature and salinity in the upper 2000m of ocean. The robotic floats rise to the surface every 10 days and transmit data to a satellite which also determines their location.
Pielke’s Litmus Test
In 2007 Roger Pielke, Sr. suggested that ocean heat should be used not just to monitor the energy imbalance in the climate system, but as a “litmus test” for falsifying the IPCC’s AGW hypothesis... One of the world’s foremost atmospheric scientists, he has published nearly 350 papers in peer-reviewed journals, 50 chapters in books, and co-edited 9 books.Though other criteria... can be used to test the AGW hypothesis, ocean heat has one main advantage: Simplicity... Ocean heat touches on the very core of the AGW hypothesis: When all is said and done, if the climate system is not accumulating heat, the hypothesis is invalid.
It is evident that the AGW hypothesis, as it now stands, is either false or fundamentally inadequate. One may argue that ... not enough time has elapsed to falsify this hypothesis. This would be true if it were not for the enormous deficit of heat we have observed. In other words, no matter how much time has elapsed, if a projection misses its target by such a large magnitude (6x to 8x), we can safely assume that it is either false or seriously flawed."