Climate change is altering the colour of the oceans

  • Recently, a new study found that the colour of the Earth’s oceans has significantly altered over the past two decades, most likely due to human-induced climate change.
  • Over 56 per cent of the oceans, more than the total land area on the planet, has experienced such shift in colour.

Impact of the change in colour of ocean

  • As per the study, although the change in colour of the oceans doesn’t impact marine life directly.
  • It indicates that marine ecosystems are in a state of flux and they could completely go out of balance in the future which will severely affecting ocean life and humans dependent on them.
  • And changes in these ecosystems could impact how productive they are and affect how much carbon the ocean stores and how much food supply there is for fisheries.

Reasons for color in the oceans

  • In most regions across the world, the oceans appear blue or navy blue for a reason.
  • This happens due to “the absorption and scattering of light.
    • When the sunlight falls on deep and clear water, colours with longer wavelengths, such as red, yellow and green, are absorbed by the water molecules but blue and violet, which have a much shorter wavelength, are reflected back.
  • But when the water isn’t deep or clean, an ocean can appear to be of a different colour.
    • Example, along Argentina’s coastline, where major rivers merge into the Atlantic Ocean, the ocean exudes a brown tint because of dead leaves and sediments spewing from the rivers.
    • In other parts of the world, the oceans appear green, which happens due to the existence of phytoplankton on the upper surface of the water.
    • Therefore, the color of the ocean in areas where there are high concentrations of phytoplankton will appear to range from blue-green to green, depending on the type and density of the phytoplankton population that is present in those areas.

Methods used to carry out the study

  • To conduct the study, dats from NASA’s Aqua satellite was taken , which has been monitoring ocean colour since 2002 — the measurements are taken in terms of the amount of light coming off the surface of the oceans, at all seven of the different wavelengths of light, from violet to red.
  • The examination of 20 years’ worth of data indicated that in more than 50 per cent of the world’s oceans, the colour has changed.
  • And researchers used a climate model – a computer representation of the Earth.
  • This model simulated the planet’s oceans under two scenarios:
    • one with the addition of greenhouse gases,
    • the other without it.
  • The greenhouse-gas model predicted that a significant trend should show up within 20 years and that this trend should cause changes to ocean colour in about 50 percent of the world’s surface oceans almost exactly what Cael found in his analysis of real-world satellite data.

Reasons for the change in the colour of the oceans

  • The study says one of the most affected areas is the Tropical ocean regions, near the equator, where the water is turning from blue to green.
  • But this doesn’t mean that the rest of the affected areas are also turning greener.
  • “The colour changes are complex and different in different locations.
  • The findings suggest that a shift in colour is happening in those regions where the oceans are getting more stratified.
  • But because of climate change, stratification has increased, making it harder for water layers to mix with each other, which has severe consequences oceans are able to absorb less carbon dioxide from the atmosphere and the oxygen absorbed isn’t able to mix properly with cooler ocean waters below, threatening the survival of marine life.
  • Moreover, nutrients aren’t able to travel up to the surface of the oceans from below.
  • This directly impacts phytoplankton, which thrives, as mentioned before, on the upper surface of the oceans.
  • Changes in the composition of the plankton population have larger effects on the marine ecosystem.
  • Plankton has two major types:
    • phytoplankton, which are plants.
    • Zooplankton, which are animals.
  • Phytoplankton are eaten by zooplankton, which are then eaten by other marine animals such as crabs, fish and sea stars, and therefore, plankton are critical in supporting marine and freshwater food webs.


  • Changes in ocean colour reflects changes in plankton communities that will impact everything that feeds on plankton.
  • It will also change how much the ocean will take up carbon because different types of plankton have different abilities to do that.
  • There they are acting as indicator for impact of climate change in the ocean ecosystem.
  • Therefore, its is need for collaborative efforts at national and international level to fight against climate change.