Rising temperatures will change the colour of the world's oceans, making them more blue in the coming decades say scientists.
They found that increased heat will change the mixture of phytoplankton or tiny marine organisms in the seas, which absorb and reflect light.
Scientists say there will be less of them in the waters in the decades to come.
This will drive a colour change in more than 50% of the world's seas by 2100.
Phytoplankton play a hugely important role in the oceans.
As well as turning sunlight into chemical energy, and consuming carbon dioxide, they are the bottom rung on the marine food chain.
They also play an important role in how we see the oceans with our eyes.
The more phytoplankton in the water, the less blue the seas will appear, and the more likely they will be to have a greenish colour.
Previous research has shown that with warming, the oceans will see a reduction in phytoplankton in many places.
This new study models the likely impact these changes will have on the colour of the ocean and the planet as the world warms up.
"What we find is that the colour will change, probably not so much that you will see by eye, but certainly sensors will be able to pick up that there's a change," lead author Dr Stephanie Dutkiewicz from Massachusetts Institute of Technology (MIT) in Cambridge, US, told BBC News.
"And it will likely be one of the earliest warning signals that we have changed the ecology of the ocean."