Lijing Cheng, Kevin E. Trenberth, John Fasullo, Tim Boyer, John Abraham, Jiang Zhu

Science Advances

Published date March 10, 2017

Improved estimates of ocean heat content from 1960 to 2015

The ocean is the memory of all of the past climate change

Kevin Trenberth, study co-author and senior scientist at the National Center for Atmospheric Research

  • Suggests that since 1960, a staggering 337 zetajoules of energy — that’s 337 followed by 21 zeros — has been added to the ocean in the form of heat. And most of it has occurred since 1980.
  • Provides updated ocean heat content (OHC) estimates with the goal of minimizing associated sampling error
  • Performs a subsample test, in which subsets of data during the data-rich Argo era are colocated with locations of earlier ocean observations, to quantify this error
  • Results provide a new OHC estimate with an unbiased mean sampling error and with variability on decadal and multidecadal time scales (signal) that can be reliably distinguished from sampling error (noise) with signal-to-noise ratios higher than 3
  • Finds that the inferred integrated Earth energy imbalance (EEI) is greater than that reported in previous assessments and is consistent with a reconstruction of the radiative imbalance at the top of atmosphere starting in 1985
  • Finds that changes in OHC are relatively small before about 1980; since then, OHC has increased fairly steadily and, since 1990, has increasingly involved deeper layers of the ocean
  • Finds that OHC changes in six major oceans are reliable on decadal time scales
  • Finds that all ocean basins examined have experienced significant warming since 1998, with the greatest warming in the southern oceans, the tropical/subtropical Pacific Ocean, and the tropical/subtropical Atlantic Ocean

Specific numbers are as follows:

"On the basis of reconstructed temperature fields and associated error bars, monthly OHC changes within 0 to 700 and 700 to 2000 m show significant warming in the past 56 years. A stronger ocean warming trend has existed since the late 1980s for both 0- to 700- and 700- to 2000-m depths compared with the 1960s to the 1980s. The linear trend of OHC at 0- to 700-m depth is 0.15 ± 0.08 × 1022 J/year (0.09 ± 0.05 W/m2) during 1960–1991 and 0.61 ± 0.04 × 1022 J/year (0.38 ± 0.03 W/m2) during 1992–2015, a warming trend four times stronger than the 1960–1991 period. The linear trend of OHC at 700- to 2000-m depth is 0.04 ± 0.08 × 1022 J/year (0.02 ± 0.05 W/m2) in the period 1960–1991 and 0.37 ± 0.02 × 1022 J/year (0.23 ± 0.02 W/m2) from 1992 to 2015 (nine times stronger than that from 1960–1991). This indicates an accelerating heat input into both the 0- to 700-m and 700- to 2000-m layers. The acceleration is most probably linked to the increasing EEI with time. In particular, a new study shows that the recent acceleration is partly due to recovery from the volcanic eruption in 1992 (Mt. Pinatubo), which led to strong ocean cooling."