Ocean heat content

Indicator Assessment
Prod-ID: IND-350-en
Also known as: CLIM 044
Created 29 Nov 2016 Published 20 Dec 2016 Last modified 20 Dec 2016
11 min read
The warming of the oceans has accounted for approximately 93 % of the warming of the Earth since the 1950s. Warming of the upper (0–700 m) ocean accounted for about 64 % of the total heat uptake. A trend for increasing heat content in the upper ocean has become evident since the 1950s. Recent observations also show substantial warming of the deeper ocean (between depths of 700 and 2 000 m and below 3 000 m). Further warming of the oceans is expected with the projected climate change. The amount of warming is strongly dependent on the emissions scenario.

Key messages

  • The warming of the oceans has accounted for approximately 93 % of the warming of the Earth since the 1950s. Warming of the upper (0–700 m) ocean accounted for about 64 % of the total heat uptake.
  • A trend for increasing heat content in the upper ocean has become evident since the 1950s. Recent observations also show substantial warming of the deeper ocean (between depths of 700 and 2 000 m and below 3 000 m).
  • Further warming of the oceans is expected with the projected climate change. The amount of warming is strongly dependent on the emissions scenario.

What is the trend in the heat content of the global ocean?

Time series of global ocean heat content at different depths

Chart
Data sources: Explore chart interactively

Past trends

The warming of the oceans has accounted for approximately 93 % of the warming of the Earth since the 1950s [i]. Ocean heat content (OHC) has increased since around 1970 (Figure 1). Differences in the values for yearly and five-yearly averages are the result of the particular method used for spatial gap filling. The linear warming trends of the uppermost 700 m of the ocean and the 700–2 000 m layer over the time period 1955–2013 were 0.27 W/m2 and 0.39 W/m2 (per unit area of the ocean), respectively. It is likely that the ocean warmed between 700 and 2 000 m from 1957 to 2014 and between 3 000 m and the bottom of the ocean from 1992 to 2005, while trends in ocean temperature between depths of 2 000 and 3 000 m were not statistically significant [ii].

Two-thirds of the observed increase in OHC has occurred in the upper 700 m of the ocean, with increases in the layers below a depth of 700 m accounting for the remaining third. The strongest warming is found near the sea surface, with the upper 75 m having warmed by more than 0.1 °C per decade since 1971. It has been estimated that heat uptake has doubled in recent decades [iii]. At a depth of 700 m, the warming decreases to about 0.015 °C per decade [iv]. Recently, it has been determined that past increases in OHC have been substantially underestimated because of poor sampling of the Southern Hemisphere and limitations of the analysis methods [v]. These concerns have not yet been considered in the datasets presented here.

Projections

All available ocean temperature projections suggest that the global ocean will continue to warm. The largest warming is projected for the upper few hundred metres of the sub-tropical gyres, similar to the observed pattern of ocean temperature changes. Mixing and advection processes will gradually transfer the additional heat to deeper levels.

The rate of increase of OHC is approximately proportional to the global mean change in surface air temperature. Under the low-to-medium (RCP4.5) emissions scenario, half of the energy taken up by the ocean by the end of the 21st century will be by the uppermost 700 m, and 85 % will be by the uppermost 2 000 m. Projected ocean warming varies considerably across forcing scenarios. Globally averaged projected surface warming ranges from about 1 °C for RCP2.6 to more than 3 °C for RCP8.5 during the 21st century, and at a depth of 1 000 m ranges from 0.5 °C for RCP2.6 to 1.5 °C for RCP8.5 [vi].



[i] J. Hansen et al., ‘Earth’s Energy Imbalance and Implications’,Atmospheric Chemistry and Physics 11, no. 24 (22 December 2011): 13421–49, doi:10.5194/acp-11-13421-2011; M. Rhein et al., ‘Observations: Ocean’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 255–316, http://www.climatechange2013.org/images/report/WG1AR5_Chapter03_FINAL.pdf; E. L. Howes et al.,The Oceans 2015 Initiative, Part I. An Updated Synthesis of the Observed Impacts of Climate Change on the Physical and Biological Processes in the Oceans, No 02/15 March (Paris: IDDRI, 2015).

[ii] 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, no. 23 (December 2010): 6336–51, doi:10.1175/2010JCLI3682.1; S. Levitus et al., ‘World Ocean Heat Content and Thermosteric Sea Level Change (0–2000 M), 1955–2010’,Geophysical Research Letters 39 (17 May 2012): L10603, doi:10.1029/2012GL051106; J. P. Abraham et al., ‘A Review of Global Ocean Temperature Observations: Implications for Ocean Heat Content Estimates and Climate Change: Review of Ocean Observations’,Reviews of Geophysics 51, no. 3 (September 2013): 450–83, doi:10.1002/rog.20022; Rhein et al., ‘Observations: Ocean’.

[iii] Peter J. Gleckler et al., ‘Industrial-Era Global Ocean Heat Uptake Doubles in Recent Decades’,Nature Climate Change 6, no. 4 (18 January 2016): 394–98, doi:10.1038/nclimate2915.

[iv] Rhein et al., ‘Observations: Ocean’.

[v] Paul J. Durack et al., ‘Quantifying Underestimates of Long-Term Upper-Ocean Warming’,Nature Climate Change 4, no. 11 (5 October 2014): 999–1005, doi:10.1038/nclimate2389.

[vi] Karl E. Taylor, Ronald J. Stouffer, and Gerald A. Meehl, ‘An Overview of CMIP5 and the Experiment Design’,Bulletin of the American Meteorological Society 93, no. 4 (April 2012): 485–98, doi:10.1175/BAMS-D-11-00094.1; J. A. Church et al., ‘Sea-Level Change’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 1137–1216, http://www.climatechange2013.org/images/report/WG1AR5_Chapter13_FINAL.pdf; M. Collins et al., ‘Long-Term Climate Change: Projections, Commitments and Irreversibility’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 1029–1136, http://www.climatechange2013.org/images/report/WG1AR5_Chapter12_FINAL.pdf; B. Kirtman et al., ‘Near-Term Climate Change: Projections and Predictability’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 953–1028, http://www.climatechange2013.org/images/report/WG1AR5_Chapter11_FINAL.pdf.

Indicator specification and metadata

Indicator definition

  • Observed change in global ocean heat content at different depths

Units

  • Ocean heat content (Joule)

Policy context and targets

Context description

In April 2013, the European Commission (EC) presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change (COM/2013/216 final) and a number of supporting documents. The overall aim of the EU Adaptation Strategy is to contribute to a more climate-resilient Europe.

One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which will be achieved by bridging the knowledge gap and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT has been developed jointly by the EC and the EEA to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and subnational adaptation strategies and plans, and (4) adaptation case studies.

Further objectives include Promoting adaptation in key vulnerablesectors through climate-proofing EU sector policies and Promoting action by Member States. Most EU Member States have already adopted national adaptation strategies and many have also prepared action plans on climate change adaptation. The EC also supports adaptation in cities through the Covenant of Mayors for Climate and Energy initiative.

In September 2016, the EC presented an indicative roadmap for the evaluation of the EU Adaptation Strategy by 2018.

In November 2013, the European Parliament and the European Council adopted the 7th EU Environment Action Programme (7th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7th EAP is intended to help guide EU action on environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7th EAP refer to climate change adaptation.

Targets

No targets have been specified.

Related policy documents

  • 7th Environment Action Programme
    DECISION No 1386/2013/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 20 November 2013 on a General Union Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. In November 2013, the European Parliament and the European Council adopted the 7 th EU Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. This programme is intended to help guide EU action on the environment and climate change up to and beyond 2020 based on the following vision: ‘In 2050, we live well, within the planet’s ecological limits. Our prosperity and healthy environment stem from an innovative, circular economy where nothing is wasted and where natural resources are managed sustainably, and biodiversity is protected, valued and restored in ways that enhance our society’s resilience. Our low-carbon growth has long been decoupled from resource use, setting the pace for a safe and sustainable global society.’
  • 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 CLIMA: Adaptation to climate change
    Adaptation means anticipating the adverse effects of climate change and taking appropriate action to prevent or minimise the damage they can cause, or taking advantage of opportunities that may arise. It has been shown that well planned, early adaptation action saves money and lives in the future. This web portal provides information on all adaptation activities of the European Commission.
  • EU Adaptation Strategy Package
    In April 2013, the European Commission adopted an EU strategy on adaptation to climate change, which has been welcomed by the EU Member States. The strategy aims to make Europe more climate-resilient. By taking a coherent approach and providing for improved coordination, it enhances the preparedness and capacity of all governance levels to respond to the impacts of climate change.

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.

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

Uncertainties

Methodology uncertainty

See under "Methodology".

Data sets uncertainty

In general, changes related to the physical and chemical marine environment are better documented than biological changes. For example, systematic observations of sea surface temperature began around 1880. More recently, these manual measurements have been complemented by satellite-based observations that have a high resolution in time and a wide geographical coverage, as well as by Argo floats that automatically measure temperature and salinity below the ocean surface.

Recently, it has been determined that past increases in OHC have been substantially underestimated because of poor sampling of the Southern Hemisphere and limitations of the analysis methods. These concerns have not yet been considered in the datasets presented here.

Rationale uncertainty

No uncertainty has been specified

Data sources

Generic metadata

Topics:

information.png Tags:
, ,
DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CLIM 044
Temporal coverage:
information.png Geographic coverage:

Geographical areas

Contacts and ownership

EEA Contact Info

Trine Christiansen

EEA Management Plan

2016 1.4.1 (note: EEA internal system)

Dates

Frequency of updates

Updates are scheduled every 4 years
Filed under: , ,
European Environment Agency (EEA)
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