Earth's Blue Oceans Turning Green Due to Climate Change: NASA Satellite Data

Recent research has uncovered a significant and visually striking transformation in our oceans: over the past 20 years, the tropical ocean has turned greener. 

This change in hue is more than just a shift in color; it reflects underlying changes in ocean ecosystems due to climate change. 

The green coloration corresponds to an increase in phytoplankton, the microscopic plant-like organisms at the heart of the ocean's food web. 

This phenomenon is a key focus of the Plankton, Aerosol, Cloud, and Ocean Ecosystem (PACE) mission, which launched in 2024 to monitor these critical changes.

The deep-blue sea is turning a touch greener, and while this might not seem as immediate as rising sea surface temperatures, it is deeply significant. 

The color of the ocean surface is a window into the health and composition of the ecosystem beneath. 

Phytoplankton, the foundational organisms in the aquatic food web and carbon cycle, thrive in near-surface waters, and their increase is a clear indicator of broader ecological shifts driven by climate change.

A team of researchers led by B. B. Cael, a principal scientist at the U.K.’s National Oceanography Centre, has revealed that 56 percent of the global sea surface has experienced a significant color change over the past two decades. 

By analyzing data from the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA’s Aqua satellite, they discovered that much of this change involves the ocean becoming greener.

The study highlighted regions where ocean surface color changed between 2002 and 2022. 

The map used darker shades of green to represent more significant changes. 

According to Cael, these are areas where changes in the ocean ecosystem have been detected over the past 20 years. 

The research focused on tropical and subtropical regions, excluding higher latitudes, which are dark for part of the year, and coastal waters, where data can be very noisy.

Chlorophyll levels, indicated by black dots on the map, also changed over the study period, covering 12 percent of the ocean’s surface. 

Chlorophyll measurements have long been the standard for estimating phytoplankton abundance and productivity through remote sensing. 

However, these measurements typically use only a few colors in the visible light spectrum. 

The new study's values, shown in green, utilize the full spectrum of visible light, capturing more comprehensive information about the ecosystem.

A long-term data series from a single sensor is rare in remote sensing. 

The Aqua satellite, launched with a design life of six years, celebrated its 20th year in orbit in 2022. 

Cael and his team used this extensive dataset to uncover trends previously predicted by climate models but thought to require 30-40 years of data to detect using traditional chlorophyll estimates. 

By incorporating all visible light, their method confirmed the trend within 20 years.

At this stage, it is challenging to pinpoint the exact ecological changes responsible for the greening. 

The researchers suggest it could be due to different assemblages of plankton, more detrital particles, or other organisms such as zooplankton. 

Cael noted that it is unlikely the color changes are due to materials like plastics or pollutants, as they are not widespread enough to impact large-scale observations.

Cael also pointed out that the ocean has become more stratified in the last 20 years. 

Surface waters have absorbed excess heat from the warming climate, making them less likely to mix with deeper, nutrient-rich layers. 

This condition favors plankton adapted to nutrient-poor environments. 

The areas of color change in the ocean align with regions that have become more stratified, but not with areas of sea surface temperature changes.

More insights into Earth’s aquatic ecosystems are expected with the launch of NASA’s PACE satellite in 2024. 

PACE will provide observations in finer color resolution, enabling researchers to infer more about ocean ecology, such as phytoplankton species diversity and growth rates. 

As our understanding of these changes grows, so does the urgency to address the root causes of climate change and protect our planet's delicate ecosystems.