Climate change affects many different ecosystems and processes in the world. Ocean warming, ocean acidification, coral bleaching events, erratic benthic migration, and changes in global ocean currents are just some of the changes researchers have measured as the world’s largest bodies of water respond to global warming.
Climate change and the changing colors of Earth’s water systems
Color change is another pattern that appears as a result of climate change. A study published in 2020 found that climate change is the driving force behind an increase in snow algae blooms in Antarctica that cause snow to seasonally turn green, orange and red. In a separate study, a team of researchers analyzed Landsat images over a period of 38 years and found that a large number of large American rivers are changing colors.
Climate change and phytoplankton
Climate change also affects phytoplankton. These microscopic marine algae are sensitive to changes in ocean temperature and salinity. The appearance of color in the ocean is affected by what is or is not in the water.
Ocean water molecules absorb all parts of the light except blue, which is reflected. Barren deep-ocean regions appear dark blue from space. Phytoplankton contain chlorophyll, a pigment that absorbs mostly the blue parts of sunlight to produce carbon for photosynthesis.
In the sunlit ocean layer with a higher density of phytoplankton, more green light is reflected back, giving the water a dark green color. Green-blue reflectance has been measured by satellites since the late 1990s.
Analyzing 20 years of satellite data to map where ocean color is changing
The latest study analyzed ocean color and found that climate changes are affecting ocean ecosystems. A study led by B.B. Kyle, a senior scientist at the United Kingdom’s National Oceanographic Center, analyzed 20 years’ worth of NASA ocean color data from 2000 to 2022 from the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on Aqua satellite board. The researchers primarily looked at the color of ocean surface waters in tropical and subtropical regions. Waters at higher latitudes tend to be darker, and ocean waters near coasts contain too much data noise to be resolved.
The analysis was able to map areas of the oceans where chlorophyll, the substance that makes plants green, had changed. For remote sensing scientists, chlorophyll levels have been the primary indicator for assessing the quantity and productivity of phytoplankton.
What the study found was that 56% of the ocean surface changed color during that time period, especially in areas near the equator. Factors such as changes in the depth of the ocean’s mixed layer or how the layers of water at the top of the ocean form are known to affect the structure and amount of plankton in the ocean, which in turn affects the color of the ocean. These trends are more pronounced in tropical and subtropical regions with less annual variation.
The researchers also wanted to know if the changes they observed in ocean color were caused by climate change. To find out, they used a complex computer model that simulates the ocean ecosystem and how it might change due to rising levels of greenhouse gases. They compared this model with actual satellite data. The model suggests that changes in ocean color could become noticeable in 20 years or less in about 46% of the ocean, which is close to the 56% change in ocean color they found when analyzing satellite data.
A 2019 study used satellite measurements of reflected light to measure the effects of climate change on phytoplankton
A previous study published by researchers from MIT and the University of Southampton in 2019 also analyzed how satellite measurements of reflected light can be used to predict the impact of climate change on phytoplankton. Using a model of ocean physics, biogeochemistry and ecosystem modified to include measurements of reflected light, the researchers modeled a 3°C increase in global temperature by 2100 to predict the impact on phytoplankton.
The model predicted that 50% of the world’s oceans would change color as subtropical regions became bluer (and devoid of phytoplankton) while polar regions would become greener as warmer waters became more hospitable to phytoplankton.
More study is needed on the impact of climate change on ocean color
The authors of the 2023 study point out that a change in ocean color has the potential to have a ripple effect on marine life, especially phytoplankton, which are sensitive to light conditions. Any changes in lighting conditions can change the entire marine ecosystem. More study is needed to understand the ramifications of color change in the world’s oceans.
This article was originally published on February 4, 2019 and has been updated with more recent research.
Cael, B.B., Bisson, K., Boss, E., Dutkiewicz, S., & Henson, S. (2023). Global climate change trends are detected in ocean environment indicators. nature, 619(7970), 551-554. https://doi.org/10.1038/s41586-023-06321-z
Dorman, L. (2023, October 2). Climate change is adding new color to the ocean. NASA Earth Observatory. https://earthobservatory.nasa.gov/images/151894/climate-change-lends-new-color-to-the-ocean
Dutkiewicz, S., Hickman, A. E., Jahn, O., Henson, S., Beaulieu, C., & Monier, E. (2019). Ocean color signature on climate change Nature Communications, 10(1), 578. https://doi.org/10.1038/s41467-019-08457-xMuch of the ocean’s surface will change color by the end of the 21st century: study MIT News