Ocean heat content

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Ocean heat content (OHC), NOAA 2012
Oceanographer Josh Willis discusses the heat capacity of water, performs an experiment to demonstrate heat capacity using a water balloon and describes how water's ability to store heat affects Earth's climate.
This animation uses Earth science data from a variety of sensors on NASA Earth observing satellites to measure physical oceanography parameters such as ocean currents, ocean winds, sea surface height and sea surface temperature. These measurements can help scientists understand the ocean's impact on weather and climate. (in HD)

Oceanic heat content (OHC) is the heat stored in the ocean. Oceanography and climatology are the science branches which study ocean heat content. The changes in the ocean heat play an important role in sea level rise, because of thermal expansion. It is with high confidence that Ocean warming accounts for 90% of the energy accumulation from global warming between 1971 and 2010.[2]

Definition and measurement

It is defined as:[3]

H=\rho c_{p}\int _{{h2}}^{{h1}}T(z)dz

\rho - water density, c_{p} - sea water specific heat capacity, h2 - bottom depth, h1 - top depth, T(z) - temperature profile.

OHC is computed from temperature measurements, often taken with a Nansen bottle. The ARGO float project deployed 3000 floaters around the worlds Ocean, which periodically dive to take temperature and salinity measurements. The World Ocean Database Project is the largest database for temperature profiles from all of the world’s oceans.

Recent changes

refer to caption
The increase in ocean heat content is much larger than any other store of energy in the Earth’s heat balance over the two periods 1961 to 2003 and 1993 to 2003, and accounts for more than 90% of the possible increase in heat content of the Earth system during these periods.[1]

Several studies in recent years, found a multidecadal increase in OHC of the deep and upper ocean regions and attribute the heat uptake to anthropogenic warming.[4] Studies based on ARGO indicate that ocean surface winds change ocean heat vertical distribution.[5] Especially the subtropical trade winds in the Pacific ocean have provided a mechanism for vertical heat distribution. The effect are changes in the ocean currents, increasing the subtropical overturning, which are also related to the El Niño and La Niña phenomenon. Depending on stochastic natural variability fluctuations, during La Niña years around 30% more heat from the upper ocean layer is transported into the deeper ocean. Model studies indicate that ocean currents transport more heat into deeper layers during La Niña years, following changes in wind circulation.[6] Years with increased ocean heat uptake have been associated with negative phases of the interdecadal Pacific oscillation (IPO).[7] This has become of particular interests to climate scientist who use the data to estimate the ocean heat uptake.

See also

References

  1. ↑ Bindoff, N.L., et al.. "Ch. 5: Observations: Oceanic Climate Change and Sea Level". Sec 5.2.2.3 Implications for Earth’s Heat Balance. , in IPCC AR4 WG1 2007, referred to by: Climate Graphics by Skeptical Science: Global Warming Components:. Skeptical Science. Components of global warming for the period 1993 to 2003 calculated from IPCC AR4 5.2.2.3. 
  2. ↑ IPCC AR5 WG1 (2013). PDF Summary for policymakers. 
  3. ↑ Dijkstra, Henk A. (2008). Dynamical oceanography ([Corr. 2nd print.] ed.). Berlin: Springer Verlag. p. 276. ISBN 9783540763758. 
  4. ↑ Abraham et al. (2013). A review of global ocean temperature observations: Implications for ocean heat content estimates and climate change. doi:10.1002/rog.20022. 
  5. ↑ Balmaseda, Trenberth & Källén (2013). Distinctive climate signals in reanalysis of global ocean heat content. doi:10.1002/grl.50382.  Essay
  6. ↑ Meehl et al. (2011). [AbstractDiscussion Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods]. doi:10.1038/nclimate1229. 
  7. ↑ Rob Painting (2013). A Looming Climate Shift: Will Ocean Heat Come Back to Haunt us?. 
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