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Climate change turning blue oceans bluer and green oceans greener

Harry Pettit, February 11, 2019 7:00PM The Sun

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An outbreak of blue-green algae at Qingdao, China in 2008. media_cameraAn outbreak of blue-green algae at Qingdao, China in 2008.


Reading level: green

Earth’s oceans will intensify* in colour or even change colour by the end of this century as climate change affects the planet, a study has predicted.

Rising global temperatures will mean that over half the world’s waters will shift colour by 2100, according to the report.

This is because warmer waters will change how populations of tiny aquatic creatures called algae grow.

Blue regions such as the subtropics* will become even more blue, as algae – also known as phytoplankton – are killed off by heat.

Green regions – such as areas near the poles – will turn a deeper green as warmer temperatures trigger huge blooms* of the small organisms, according to the study.

The colour changes are just the visual signs of major changes that will flow through the Earth’s ecosystems*, scientists warned.

“It could be potentially quite serious,” warned Dr Stephanie Dutkiewicz, from the Massachusetts Institute of Technology, US.

“If climate change shifts one community of phytoplankton to another, that will also change the types of food webs they can support.”

Algae reflects green light, and so causes the oceans to appear greener when pictured from space.

Plankton media_cameraA bloom of phytoplankton in the Black Sea seen from the International Space Station.

Climate experts created a computer model that predicted how the creatures may grow and change the colour of our planet in the event of extreme climate change.

It looks at how the sea’s colour might change if the global temperature has risen 3C by 2100.

The changes were dramatic, with large areas of the oceans turning green by the end of the century.

Hawksbill Turtle media_cameraA Hawksbill sea turtle swimming with fish in the tropical ocean around Thailand. Blue water like this could appear even more blue if the temperature kills the normal population levels of algae. Picture: Istock

“The changes won’t appear huge to the naked eye*, and the ocean will still look like it has blue regions in the subtropics and greener regions near the equator and poles,” said Dr Dutkiewicz.

“But it’ll be enough difference that it will affect the rest of the food web that phytoplankton supports.”

This story originally appeared on The Sun and is republished with permission.


  • intensify: get stronger or more intense
  • subtropics: climate zone between tropics and temperate
  • blooms: grows quickly
  • ecosystems: communities of living things
  • naked eye: what you can see without the help of a telescope or microscope


Rising temperatures in colour

King penguins at risk of dying out

Sir David Attenborough’s climate change warning

Climate change could ruin holidays?


  1. What is another name for phytoplankton?
  2. What happens when phytoplankton gets too hot?
  3. What colour are the oceans around the poles? What colour in subtropical regions?
  4. In which country is the university mentioned in the story?
  5. What colour light does algae reflect?


1. Cause and Effect Chart
What are the CAUSES and EFFECTS of the changes to phytoplankton in our oceans? Create a flowchart or visual diagram that will help other students understand this.

Time: allow 25 minutes to complete this activity
Curriculum Links: Science, English

2. Extension
Imagine that you are the science reporter for Kids News. You want to know more about this story. Write five questions that you would like to ask Dr Stephanie Dutkiewicz. Next to each question, write down why you think that this is an important question.

Time: allow 20 minutes to complete this activity
Curriculum Links: Science, English, Critical and Creative Thinking

Synonym Word Volley – Colours

This article focuses on the sea changing colour over the next century – but their description of the colours doesn’t really help us visualise the changes. What more specific words could they use to describe the type of green or blue the sea might change too, rather than greener and even more blue?

Let’s see how well you know your colours.

Partner up and ‘volley’ colours back and forth to each other until someone can’t add a new colour. You have 5 seconds to answer before you are out. Don’t just stick with the basic colours, you’ll need to go further. Think jade, turquoise, aquamarine etc.

How many did you get? Could any of the colours you came up with be used in the article?

HAVE YOUR SAY: What can children do to look after our planet? Share your best ideas.
No one-word answers. Use full sentences to explain your thinking.

Extra Reading in environment