4sea, Oceans

The state of the oceans in the wake of the changing climate

 This article is part of the 4sea Project

The oceans and climate change

It is not often that we think about what a huge impact the oceans have on the climate. When we talk about climate change the images that conjure up in people’s minds are often linked to the temperature rise and the greenhouse gas concentrations in the atmosphere, and therefore to extreme weather events, melting glaciers, loss of biodiversity and other similar phenomena linked to changes up in the air. Thus, the state of the oceans is often dismissed, not because of a lack of interest, but often because of the sheer complexity and obscurity of these huge masses of water that in many ways remain a mystery for most people. This subject hasn’t consequently been recognised in the same manner as has been the case for the state of the atmosphere in the public discussion.

The five world oceans cover up to 71 % of the earth’s surface and have therefore a defining role in how the climate system operates today.1 The oceans act as carbon and heat sinks, support a large variety of life on earth and circulate through the great ocean currents in a global conveyor belt, that largely affects the weather systems in many areas around the globe. Even though up to one third of the human induced carbon emissions have ended up in the oceans the development has not been as visual as for many other cases affected by climate change. The average global ocean temperature has increased by around 0.1 °C over the 20th century, which is distinctively less than for the average global air temperature with an increase of approximately 0,6 °C for the same time period.2 Despite the rather slow temperature development and the acidification caused by the excess greenhouse gas concentration in the atmosphere, these changes have a huge impact on both ecosystems as a whole, coastal areas and on the health of different marine species. These direct impacts will then have indirect consequences on pretty much all human societies and ecosystems around the globe. This is why it is extremely important that the correlation between the oceans and climate change is recognised in the public discussion and integrated in climate change negotiations.

The role of the oceans in the climate system

The oceans play a crucial role for the state of the global climate. The ocean currents, primarily driven by the stationary wind belts, the Coriolis effect and density differences, distribute cold and warm water across the globe, which alters weather patterns in different parts of the world. The temperature of the ocean current dictates if the coastal area is generally more dry or humid, and usually stabilises the mean annual temperature of an area. This is the case in Northern Europe where an approximately 10°C higher mean annual temperature occurs because of the warm Gulf stream that brings warm equatorial water to the higher latitudes on the Northern hemisphere.3 Also upwelling,4 which in many areas is crucial for the fisheries and for the well-being and economic stability for many nations, is largely caused by the movements of the ocean.

As the ocean heats up, the occurrence of extreme weather events such as tropical cyclones get more and more violent and frequent, which often results in devastating loss of human life as well as economic loss for the nations affected. These kinds of temperature changes also affect the distribution of precipitation patterns across the globe that will greatly affect the agricultural section and therefore the food safety for large populations.

How the oceans change because of climate change

It is evident that the oceans are changing, but how are they changing?

Since the end of the 19th century the amount of greenhouse gases in the atmosphere has risen at an unprecedented rate mainly due to human induced emissions. Therefore the concentration of mainly CO2, methane and nitrous oxide has risen from 280 parts per million to up to 400 parts per million in only 150 years, which is believed to be the main cause to the rising global temperatures.5 As the oceans act as both heat and carbon sinks, the impact on the oceans is obvious.

So far scientists have observed acidification, which is caused by the increase in dissolved carbon in the oceans that results in a changed chemical composition and therefore a lower pH. Another observation is that the global sea surface temperature has risen by approximately 1°C for the past 140 years and is expected to continually rise throughout the 21st century, primarily in the upper 100 meters of the ocean.6 Furthermore scientists have noted that climate change could alter some changes in ocean current patterns around the globe that could have imminent impacts on the climate both regionally and globally. Lastly the rising sea levels, caused by melting glaciers and ice caps as well as by the thermic expansion, has been calculated to have risen approximately 19 cm during the past decade.7


There are many different consequences that follow as a result of these different changes in the oceans that affect both ecosystems and human societies. Climate change and human pollution have altered marine and coastal ecosystems to great danger in terms of problems with adaptation to the new and quickly changing circumstances. The biodiversity has suffered and a lot of marine species are endangered or almost extinct. Coastal areas are affected by the rising sea levels as well as by the more frequent and extreme weather phenomena, whereas several marine ecosystems suffer from rising sea temperatures, acidification as well as human induced pollution. Changes in ocean current patterns could also have great consequences on weather systems in different areas, which ultimately could result in changes in the whole climate system.

There is therefore no doubt that the world oceans have suffered immense changes in both their chemical and physical composition, and continue to do so as both greenhouse gas emissions, global temperatures as well as human induced pollution have increased. In upcoming articles we will discuss these different consequences and the effects that they have on both ecosystems and human societies. In our soon-to-be published website we will also look at new initiatives and ideas to combat these problems and therefore give you some tips and ideas on what YOU can do to be a part of the solution.


About the author: Venni Arra is currently completing her bachelor’s degree in physical geography at Stockholm University and is doing her internship at CliMates in Paris for the Ocean and Climate change project 4sea.

This article has been written in the context of 4sea. 4sea, a project about the importance of the world oceans, addresses the interdependence between the oceans and climate change, entraining everyone to become ocean lovers – for now through articles and videos on this blog and in August on our own platform. 4sea is a joint project between the youth organisations CliMates, Youth for Ocean and Vitamin Sea. Love it? Stay tuned for our platform!


  1. IPCC, Oceans and shallow seas, [website], https://www.ipcc.ch/publications_and_data/ar4/wg2/en/ch4s4-4-9.html (accessed 12 June 2017)
  2. National Geographic, Sea Temperature Rise, [website], http://ocean.nationalgeographic.com/ocean/explore/pristine-seas/critical-issues-sea-temperature-rise/ (accessed 12 June 2017 )
  3. Bjerknes Center for Climate Research, The Gulf Stream and our mild climate in Norway, [website], 2015, http://www.bjerknes.uib.no/en/article/ipcc/gulf-stream (accessed 10 June 2017)
  4. National Ocean Service, What is upwelling?, [website], 2015, http://oceanservice.noaa.gov/facts/upwelling.html (accessed 12 June 2017)
  5. NASA, A blanket around the Earth, [website], https://climate.nasa.gov/causes/ (accessed 12 June 2017)
  6. European Environment Agency, Rising sea surface temperature: towards ice-free Arctic summers and a changing marine food chain, [website], 2015, https://www.eea.europa.eu/themes/coast_sea/sea-surface-temperature/rising-temp (accessed 12 June 2017)
  7. Church, J.A. et al., 2013: Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Join the conversation

Entrez vos coordonnées ci-dessous ou cliquez sur une icône pour vous connecter:

Logo WordPress.com

Vous commentez à l'aide de votre compte WordPress.com. Déconnexion /  Changer )

Photo Google+

Vous commentez à l'aide de votre compte Google+. Déconnexion /  Changer )

Image Twitter

Vous commentez à l'aide de votre compte Twitter. Déconnexion /  Changer )

Photo Facebook

Vous commentez à l'aide de votre compte Facebook. Déconnexion /  Changer )


Connexion à %s