Detecting climate change trends through ocean color changes

New research uncovers the potential of ocean color as an indicator of global climate change.

Climate change impacts are being tracked with increasing precision and creativity. One such novel approach involves observing the color changes in our oceans, it’s turning green.

“To investigate possible trends in ocean colour, we performed such an autocorrelation-corrected multivariate regression on the first 20 years of MODIS-Aqua ocean Rrs data, spanning July 2002–June 2022 (Methods). We find significant trends, here defined as a signal-to-noise ratio (SNR) higher than two, in 56% of the ocean, primarily equatorward of 40°”

Cael, B.B., Bisson, K., Boss, E. et al. Global climate-change trends detected in indicators of ocean ecology. Nature (2023).

The recent study published in the scientific journal, Nature, leverages two decades of satellite data to uncover significant climate change trends reflected in alterations of ocean color. This study has implications not only for understanding climate change impacts but also for marine conservation and governance.

Unlocking the potential of ocean color

Satellite remote sensing is an effective means of obtaining time series of marine ecosystems on a global scale. Ocean color satellites measure the amount of light radiating from the ocean and atmosphere, collecting global measurements for decades.

This color, scientifically known as remote-sensing reflectance (Rrs), can provide insights into the state of surface-ocean ecosystems, making it an ‘essential climate variable’ according to the Global Climate Observing System.

Challenges in detecting climate change trends

Traditional methods of detecting climate change-driven trends have relied on data points like chlorophyll a (Chl), which provides information on the abundance of phytoplankton.

However, detecting trends in Chl requires more than 30 years of data even on regional scales. On the other hand, using Rrs for detecting trends is known to be more sensitive and rapid, as Rrs is multivariate and some wavebands have low interannual variability.

The intensity of the purple color indicates the SNR. Black stippling indicates regions with significant trends in Chl as well (12% of the ocean). MODIS-Aqua data from July 2002 to June 2022.

Unearthing trends from two decades of data

By leveraging a 20-year Rrs time series from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite, the researchers found significant trends in Rrs for 56% of the global surface ocean. Their analysis shows that these changes in Rrs are not related to changes in sea surface temperature, suggesting that other climate-driven factors might be affecting ocean color.

Cumulative distribution function of the ToE of the ocean-colour trend in the model simulation. The orange point indicates the fraction of the total surface-ocean area with a significant trend in the 20-year MODIS-Aqua time series.

Call for continued satellite missions

The results of this study underscore the value of long-term satellite missions like MODIS-Aqua, and the researchers urge space agencies to maintain missions for as long as feasible. The significant trends occurring where interannual variability is low imply that similar signals may be expected to emerge in other portions of the ocean in the coming years.

Implications of climate change on marine ecosystems

The observed changes in Rrs could potentially impact the role of plankton in marine biogeochemical cycles and ocean carbon storage, as well as plankton consumption by higher trophic levels and fisheries. This knowledge of where the surface-ocean microbial ecosystem is changing might be useful for identifying regions of the open ocean in which to establish marine protected areas. Detecting change in these ecosystems is thus of great utility.

Conclusion: tracking climate change through the color of our oceans

This research brings a unique perspective on the long-term implications of climate change impacts, stressing the need for continuous observation and data collection. The study’s revelation of climate change trends through ocean color not only enhances our understanding of the far-reaching impacts of climate change but also demonstrates the way for new approaches in marine conservation and governance.

Through such data-driven insights, we can better prepare for and navigate our way in a world shaped by climate change.


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