Ocean-Climate Nexus

Ocean-Climate Nexus

By Sabrina Speich, Professor, Ecole Normale Supérieure, and Weidong Yu, Professor, Sun Yat-Sen University

The ocean is a thin layer of saltwater that envelopes 71% of the Earth and contains 96% of its water. It contains the most varied biodiversity on the planet and is responsible for around 50% of gross primary production. It also acts as the Earth’s thermostat, absorbing and transforming a significant portion of the radiation from the sun that reaches the Earth’s surface. It provides water vapour to and exchanges heat with the atmosphere, shaping the Earth’s weather and climate and its variability over a range of time scales, from hours to millennia. It mitigates climate change by absorbing almost all the excess heat (89%: Von Schuckmann et al., 2020) and a quarter of the CO2 (Friedlingstein et al., 2020) produced by human activities.

The ocean receives heat from the sun electromagnetic radiation, mainly in the tropical regions. There is a constant back and forth exchange of water, energy and carbon between the ocean surface and the atmosphere at all latitudes where it is not ice-covered. The ocean is not static and ocean currents redistribute the excess heat received in the tropics towards higher latitudes, and towards the deep ocean. This transport is stronger at high latitudes – in polar regions – where surface waters become denser and sink, mainly due to high heat losses. The time scale of the transport and redistributions is highly variable, from season or year in tropical regions to a decade in the surface layers, and several hundred years, even thousands of years in the deep layers.

The global transport of heat, fresh water and carbon through the ocean is not only comparable in size to that of the atmosphere, but the ocean is the main reservoir of these properties for the atmosphere. The continuous ocean-atmosphere exchange of these properties and their storage in the ocean makes the ocean a key regulator of weather and climate at every time scale (from minutes to millennia: e.g., Smith et al., 2012; Doblas-Reyes et al., 2013; Kirtman et al., 2013; Meehl et al., 2014), extending the predictability of the Earth system at these scales. Seasonal and decadal prediction systems rely principally on accurately forecasting the fast dynamic and slow ocean modes of variability and their role in modulating the atmosphere (Kirtman et al., 2013). In order to ensure skilful – useful – predictions, models must be initialized with the ocean observations.

Timely and sustained ocean observations, both satellite and in situ, are crucial for the development of skilful predictions that meet societal expectations and needs (Smith et al., 2012). Much of the information underlying such predictions comes from globally-coordinated ocean basin scale observing systems. Major international weather and climate forecasting groups, including the European Centre for Medium-Range Weather Forecasts (ECMWF), the U.S. National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) and WMO, have requirements for ocean information to enable a resilient and sustainable blue economy. In addition, there is growing public recognition of the critical importance of information on current and future ocean conditions to meet diverse user needs. These include better observation and forecasting of waves, currents, sea level, water quality and the abundance of living marine resources as well as improved marine, weather and climate prediction services.


Doblas-Reyes, F. J., GarcíaSerrano, J., Lienert, F., Biescas, A. P., and Rodrigues, L. (2013). Seasonal climate predictability and forecasting: status and prospects. WIREs Clim. Change 4, 4245–4268. doi: 10.1002/wcc.217

Friedlingstein, P., et al.(2020) Global Carbon Budget 2020, Earth Syst. Sci. Data, 12, 3269–3340, https://doi.org/10.5194/essd-12-3269-2020.

Kirtman, B., Stockdale, T., and Burgman, R. (2013). “The Ocean’s role in modeling and predicting seasonal to-interannual climate variations,” in Ocean Circulation and Climate: A 21st Century Perspective, 2nd Edn eds G. Siedler, S. Griffies, J. Gould, and J. Church (Sydney: Academic Press), 625–643. doi: 10.1016/b978-0-12-391851-2.00024-6

Meehl, G. A., Goddard, L., Boer, G., Burgman, R., Branstator, G., Cassou, C., et al. (2014). Decadal climate prediction an update from the trenches. Bull. Am. Meteorol. Soc. 95, 243–267. doi: 10.1175/BAMS-D-12-00241.1

Smith, D. M., Scaife, A. A., and Kirtman, B. (2012). What is the current state of scientific knowledge with regard to seasonal and decadal forecasting. Environ. Res. Lett. 7:015602. doi: 10.1088/1748-9326/7/1/015602

von Schuckmann, K., et al. (2020). Heat stored in the Earth system: where does the energy go? Earth Syst. Sci. Data, 12(3), 2013–2041. https://doi.org/10.5194/essd-12-2013-2020 

The Role of the Ocean in a Changing Climate

All life on Earth depends directly or indirectly on the ocean and cryosphere (cryosphere is the term for the portion of the Earth where water is frozen). The ocean and cryosphere support unique habitats, and are interconnected with other components of the Earth system through the global exchange of water, energy and carbon.

Global Climate Indicators: Ocean heat content, acidification, deoxygenation and blue carbon

WMO has published annual State of the Global Climate reports since 1993. In 2020, it published a five-year climate report for 2015 to 2019 incorporating data and analyses from the State of the Global Climate across this period. The initial purpose of the annual report was to inform Members on climate trends, extreme events and impacts. In 2016, the purpose was expanded to include summaries on key climate indicators to inform delegates in Conference of Parties (COP) of the United Nations Framework Convention on Climate Change (UNFCCC).

Climate and Ocean research: The World Climate Research Programme (WCRP)

International ocean research is largely coordinated through the International Oceanographic Commission (IOC) of UNESCO, International Science Council (ISC) and WMO and their partnerships. WMO has significant interests in the development and delivery of ocean information to underpin the breadth of research, applications and services delivered by its Members, thus the Organization is involved in a range of ocean activities. The World Climate Research Programme, co-sponsored by WMO, IOC-UNESCO and International Science Council (ISC), offers a prime example of this coordination and partnership in climate research.