Ocean heat content (CLIM 044) - Assessment published Nov 2012

Key policy question: What is the trend in the heat content of the global ocean?

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.

Data source:

• Ocean heat content calculated based on observations made in the upper 700 m of the water column (1955 – 2011) provided by National oceanic and atmospheric administration (NOAA)

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Key assessment

Past trends

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

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.