Estimating global ocean heat content changes in the upper 1800 m since 1950 and the influence of climatology choice

With the buildup of greenhouse gasses in the atmosphere, more energy enters the top of the atmosphere than escapes. About 93% of this energy imbalance has warmed the ocean, with about 3% warming the land, 3% melting ice, and 1% warming and adding moisture to the atmosphere. Warmed oceans also expand, raising sea level. Hence, understanding how much energy is being stored by the oceans and where is important to understanding how much and how fast the Earth will warm and sea level will rise.

Over the last six decades, ocean temperature has been measured over increasing areas of the ocean and to greater depths using a succession of instruments. Recently, the Argo array of profiling floats provides year-round high-quality near-global data over the upper half of the ocean volume, a revolutionary advance that allows careful re-evaluation of the sparser, often shallower, historical data. Here, globally averaged ocean temperature anomalies are estimated at annual intervals from the surface to 1800-m depth in five different layers using gridding parameters determined by ocean data characteristics. The shallowest 0-100 m layer is 50% sampled from 1956 onward, while the deepest 900-1800 m layer doesn't reach that coverage until 2004. In addition, the choice of a warmer modern climatology versus a colder historical one can alter the estimated ocean warming when gaps in data coverage are filled with zero anomalies, a common assumption. The choice of climatology does not affect the estimated warming when gaps are filled with the mean ocean temperature anomaly of the sampled areas.