Ocean heat content (CLIM 044) - Assessment published Nov 2012
Climate change (Primary topic)
Coasts and seas
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CLIM 044
Key policy question: What is the trend in the heat content of the global ocean?
- The warming of the World Ocean accounts for approximately 93 % of the warming of the Earth system during the last 6 decades.
- An increasing trend in the heat content in the uppermost 700 m depth of the World Ocean is evident over the last 6 decades. Recent observations show substantial warming also of the deeper ocean (between 700 m and 2 000 m depth).
- Further warming of the oceans is expected with projected climate change, but quantitative projections of ocean heat content are not available.
Ocean heat content calculated based on observations made in the upper 700 m of the water column
Note: Ocean heat content is defined as the integrated temperature change times the density of seawater, times specific heat capacity from the surface down to the deep ocean.
- Ocean heat content calculated based on observations made in the upper 700 m and 2000 m of the water column provided by National oceanic and atmospheric administration (NOAA)
The warming of the World Ocean accounts for approximately 90 % of the warming of the Earth during the last 6 decades [i].
Figure 1 shows that the heat content of the World Ocean has increased since around 1970. The linear trend over the whole time series 1955–2010 of the uppermost 700 m and 2 000 m layer was 0.27 Wm-2 and 0.39 Wm-2 (per unit area of the World Ocean), respectively. Two thirds of the observed increase of global heat content has occurred in the upper 700 m of the ocean, with increases in the layers below 700 m depth accounting for the remaining one third [ii]. Heat content has increased in all major sea basins of the World Ocean, in particular in the Atlantic Ocean.
Several global ocean data assimilation products are available to compare observation-based estimates with independent reanalysis data. Global and basin-scale heat content warming trends in the upper 700 m of the ocean computed from a set of global ocean reanalyses fall within the range of the most recent observation-based estimates derived using different methods [iii].
Projections of OHC are very uncertain and are hence not included here.
[i] John A. Church et al., „Revisiting the Earth’s sea-level and energy budgets from 1961 to 2008“, Geophysical Research Letters 38, Nr. 18 (September 16, 2011), doi:10.1029/2011GL048794; J. Hansen et al., „Earth’s energy imbalance and implications“, Atmospheric Chemistry and Physics 11, Nr. 24 (Dezember 22, 2011): 13421–13449, doi:10.5194/acp-11-13421-2011; S. Levitus et al., „World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010“, Geophysical Research Letters 39, Nr. 10 (Mai 17, 2012), doi:10.1029/2012GL051106.
[ii] J.E. Dore et al., „Physical and biogeochemical modulation of ocean acidification in the central North Pacific“, Proceedings of the National Academy of Sciences 106 (2009): 12235–12240., doi:10.1073/pnas.0906044106; S. Levitus u. a., „Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems“, Geophysical Research Letters 36, Nr. 7 (April 11, 2009), doi:10.1029/2008GL037155; Levitus et al., „World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010“; Sarah G. Purkey and Gregory C. Johnson, „Warming of global abyssal and deep southern ocean waters between the 1990s and 2000s: Contributions to global heat and sea level rise budgets“, Journal of Climate 23, Nr. 23 (Dezember 2010): 6336–6351, doi:10.1175/2010JCLI3682.1.
[iii] John M. Lyman et al., „Robust warming of the global upper ocean“, Nature 465, Nr. 7296 (Mai 2010): 334–337, doi:10.1038/nature09043; Simona Masina u. a., „Global ocean re-analyses for climate applications“, Dynamics of Atmospheres and Oceans 52, Nr. 1–2 (September 2011): 341–366, doi:10.1016/j.dynatmoce.2011.03.006.
Ocean heat content calculated based on observations made in the upper 700 m and 2000 m of the water column
provided by National oceanic and atmospheric administration (NOAA)
More information about this indicator
See this indicator specification for more details.