It is virtually certain that the upper ocean (0 to 700 m) warmed from 1971 to 2010. This result is supported by three independent and consistent methods of observation including (1) multiple analyses of subsurface temperature measurements described here; (2) SST data (Section 2.4.2) from satellites and in situ measurements from surface drifters and ships; and (3) the record of sea level rise, which is known to include a substantial component owing to thermosteric expansion (Section 3.7 and Chapter 13). The warming rate is 0.11 [0.09 to 0.13]°C per decade in the upper 75 m, decreasing to about 0.015°C per decade by 700 m. It is very likely that surface intensification of the warming signal increased the thermal stratification of the upper ocean by about 4% (between 0 and 200 m depth) from 1971 to 2010. It is also likely that the upper ocean warmed over the first half of the 20th century, based again on these same three independent and consistent, although much sparser, observations. Deeper in the ocean, it is likely that the waters from 700 to 2000 m have warmed on average between 1957 and 2009 and likely that no significant trend was observed between 2000 and 3000 m from 1992 to 2005. It is very likely that the deep (2000 m to bottom) North Atlantic Ocean north of 20°N warmed from 1955 to 1975, and then cooled from 1975 to 2005, with an overall cooling trend. It is likely that most of the water column south of the Sub-Antarctic Front warmed at a rate of about 0.03°C per decade from 1992 to 2005, and waters of Antarctic origin warmed below 3000 m at a global average rate approaching 0.01°C per decade at 4500 m over the same time period. For the deep ocean, sparse sampling is the largest source of uncertainty below 2000 m depth.