Ocean heat content

Assessment versions

Published (reviewed and quality assured)

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

Justification for indicator selection

The World Ocean is the dominant component of the Earth’s heat balance. Oceans cover roughly 72 % of the planet’s surface, and water has a heat uptake capacity that is around 20 times greater than that of the atmosphere. About 90 % of the total warming caused by climate change is manifested in increased global heat content. Hence, a precise estimate of Ocean Heat Content (OHC) is essential for understanding the role of oceans in past climate change, and for assessing future climate change. OHC is defined as the integrated temperature change times the density of sea water, times specific heat capacity from the surface down to the deep ocean. Estimates of it are made based on temperature measurements or on reanalyses made using a combination of models and observations.

Changes in heat content also cause the ocean to expand or contract, thereby changing sea level regionally and globally. This thermosteric effect has contributed about one quarter to global sea-level rise since 1993.

Scientific references:

• IPCC 2007: Climate Change: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. (S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller, eds.). Cambridge University Press, Cambridge.

Indicator definition

• Ocean heat content

Units

• Joules (J)

Policy context and targets

Context description

Targets

No targets have been specified.

Related policy documents

• Climate-ADAPT: Mainstreaming adaptation in EU sector policies
  Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
• Climate-ADAPT: National adaptation strategies
  Overview of activities of EEA member countries in preparing, developing and implementing adaptation strategies
• DG Climate Action: What is the EU doing about climate change?
  Activities of the EU regarding climate change (both mitigation and adaptation)
• White paper - Adapting to climate change: towards a European framework for action
  EU framework for adaptation to climate change, leading to a comprehensive EU adaptation strategy by 2013

Methodology

Methodology for indicator calculation

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. It is calculated here base on observations from the upper 700 metres of ocean water.

The warming of the world ocean since 1955 is estimated using different kinds of observational data: historical data not previously available, additional modern data, correcting for instrumental biases of bathythermograph data, and correcting or excluding some Argo float data.

Methodology for gap filling

Not applicable

Methodology references

• Levitus et al. 2009: Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems. Levitus, S., Antonov, J. I., Boyer, T. P., Locarnini, R. A., Garcia, H. E. and Mishonov, A. V. (2009) Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems. Geophysical Research Letters 36(7). doi:10.1029/2008GL037155

Data specifications

EEA data references

• No datasets have been specified here.

External data references

• Ocean heat content calculated based on observations made in the upper 700 m of the water column (1955 – 2011)

Data sources in latest figures

Uncertainties

Methodology uncertainty

Not applicable

Data sets uncertainty

Ocean temperature data are sparse in the polar and subpolar regions of the world. In general, however, changes related to the physical and chemical marine environment are better documented than biological changes because links between cause and effect are better understood and often time series of observations are longer. For example, systematic observations of both sea-level and sea surface temperature were started around 1880 and are today complemented by observations from space that have high resolution in time and geographical coverage and by Argo floats that also automatically measure temperature and salinity below the ocean surface.

Further information on uncertainties is provided in Section 1.7 of the EEA report on Climate change, impacts, and vulnerability in Europe 2012 (http://www.eea.europa.eu/publications/climate-impacts-and-vulnerability-2012/)

Rationale uncertainty

No uncertainty has been specified