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Increasing heat content of the global ocean dominates the energy imbalance in the climate system 1 . Here we show that ocean heat gain over the 0-2,000 m layer continued at a rate of 0.4-0.6 W m −2 during 2006-2013. The depth dependence and spatial structure of temperature changes are described on the basis of the Argo Program's 2 accurate and spatially homogeneous data set, through comparison of three Argo-only analyses. Heat gain was divided equally between upper ocean, 0-500 m and 500-2,000 m components. Surface temperature and upper 100 m heat content tracked interannual El Niño/Southern Oscillation fluctuations 3 , but were o set by opposing variability from 100-500 m. The net 0-500 m global average temperature warmed by 0.005 • C yr −1 . Between 500 and 2,000 m steadier warming averaged 0.002 • C yr −1 with a broad intermediate-depth maximum between 700 and 1,400 m. Most of the heat gain (67 to 98%) occurred in the Southern Hemisphere extratropical ocean. Although this hemispheric asymmetry is consistent with inhomogeneity of radiative forcing 4 and the greater area of the Southern Hemisphere ocean, ocean dynamics also influence regional patterns of heat gain.Global ocean sampling of water-column temperature in the twentieth century was spatially and temporally sparse 5 , characterized by strong coverage biases towards the Northern Hemisphere, towards the continental coastlines, and seasonally towards summer. Roughly half a million temperature/salinity profiles to at least 1,000 m were collected by research vessels, mostly in the past 50 years. Additional lower accuracy and shallower temperature-only data have been obtained from commercial and naval vessels. These help to mitigate the coverage deficiencies but raise additional concerns regarding measurement bias errors 6 .Today the Argo Program 2 provides systematic coverage of global ocean temperature/salinity from 0-2,000 m using 3,500 autonomous profiling floats spaced about every 3 • of latitude and longitude, each providing a temperature/salinity profile every 10 days. Profiling float technology 7 allows data to be collected without a ship by long-lived free-drifting instruments. Argo has collected 1.2 million temperature/salinity profiles and continues to provide 10,000 profiles per month, with far greater spatial and temporal homogeneity than that achieved historically. Previous investigations of ocean heat content 5 have combined Argo and historical data of variable quality, and these studies have been impacted by coverage and measurement bias issues. Here we estimate ocean heat gain over the 2006-2013 period for which Argo coverage is global (Methods), and through the exclusive use of Argo data with uniformly high quality.Argo's ocean temperature data set is invaluable for estimating the net radiation balance of the Earth. The deduced excess of downward over outgoing radiation 8 driving global warming is too small to measure directly as radiative fluxes 9 . About 93% of this net planetary energy increase is stored in the oceans 1 , a result of the ...

[1] The evolution of ocean temperature measurement systems is presented with a focus on the development and accuracy of two critical devices in use today (expendable bathythermographs and conductivity-temperature-depth instruments used on Argo floats). A detailed discussion of the accuracy of these devices and a projection of the future of ocean temperature measurements are provided. The accuracy of ocean temperature measurements is discussed in detail in the context of ocean heat content, Earth's energy imbalance, and thermosteric sea level rise. Up-to-date estimates are provided for these three important quantities. The total energy imbalance at the top of atmosphere is best assessed by taking an inventory of changes in energy storage. The main storage is in the ocean, the latest values of which are presented. Furthermore, despite differences in measurement methods and analysis techniques, multiple studies show that there has been a multidecadal increase in the heat content of both the upper and deep ocean regions, which reflects the impact of anthropogenic warming. With respect to sea level rise, mutually reinforcing information from tide gauges and radar altimetry shows that presently, sea level is rising at approximately 3 mm yr À1 with contributions from both thermal expansion and mass accumulation from ice melt. The latest data for thermal expansion sea level rise are included here and analyzed.

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