New research has found climate change is causing our oceans to switch colour from blue to green, which one co-author warned is “not surprising, but frightening”.

Researchers from the UK’s National Oceanography Centre and the Massachusetts Institute of Technology (MIT) detected that over the past 20 years, the colour of oceans around the world has changed.

The slow, but steady, colour change has been observed in 56 per cent of the Earth’s oceans, and tropical regions near the equator in particular have become more green over time.

“The colour of the ocean is a literal reflection of the organisms and materials in its waters”, MIT News said.

The study was published in Nature and came with a companion piece in which ocean and climate scientist B.B. Cael stressed that humans are impacting the ecosystem “in a way that we haven’t seen before”.

Revealing colours

“One possibility is that the shift might have something to do with how nutrients are distributed in the ocean. As surface waters warm, the upper layers of the ocean become more stratified [meaning there are more layers of ocean within the upper layers of ocean], making it harder for nutrients to rise to the surface,” Nature wrote.

“When there are fewer nutrients [in the upper layers of water], smaller phytoplankton [microscopic plant-like organisms] are better at surviving than larger ones, and so changes in nutrient levels could lead to changes in the ecosystem that are reflected in changes in the water’s overall colour.”

The fear is that even the smallest changes can have significant knock-on effects for the entire food chain.

“All changes are causing an imbalance in the natural organisation of ecosystems. Such imbalance will only get worse over time if our oceans keep heating,” Stephanie Dutkiewicz, senior research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences and the Center for Global Change Science, told CNN.

Speaking to NBC News, Dutkiewicz explained different types of plankton absorb different amounts of carbon, so the colour change could also reflect “how much the ocean will take up carbon”.

Tweet from @MITGlobalChange

Impact of climate change

The teams looked at colour variation data from 2002 to 2022 and then used climate change models to see what would happen to oceans without climate change, and with it.

The colour changes were consistent with what would happen if greenhouse gases were added to the atmosphere.

“But they are pretty sure of one thing: Human-induced climate change is likely the driver,” the news alert said.

“I’ve been running simulations that have been telling me for years that these changes in ocean colour are going to happen,” Dutkiewicz said.

“To actually see it happening for real is not surprising, but frightening. And these changes are consistent with man-induced changes to our climate.”