Over the past two decades, the colors of our oceans have been silently altering due to human-induced climate change. A study conducted by the Massachusetts Institute of Technology, the National Oceanography Center in the UK, and various other US institutions in collaboration with NASA, published in Nature, reveals this startling fact. The researchers discovered that subtle shifts in color hues have been occurring across 56% of the ocean surface - an area larger than all the landmass on Earth.
The Changing Colors Are Not Just for Aesthetics
The tropical ocean regions near the equator, in particular, have reportedly grown greener over the past 20 years. This change is beyond the natural color variability of the ocean surface. Scientists suggest that these shifts reflect alterations in surface ocean ecosystems, which are stimulated by the ongoing climate crisis.
Currently, the exact nature of this transformation is unclear. However, greener waters generally indicate the presence of phytoplankton - photosynthetic organisms, primarily cyanobacteria and unicellular algae, that dwell within the first 100 meters of ocean depth. The green hue is attributed to chlorophyll, a pigment that enables phytoplankton to utilize sunlight to absorb atmospheric CO2 and convert it into sugars.
Monitoring the Green Shift From Outer Space
Given that phytoplankton aid in supporting the marine food chain and sequestering carbon dioxide, scientists are keen on tracking its distribution and observing its response to climate change. Traditionally, they attempt to monitor chlorophyll using satellite images of oceans.
Yet, a decade ago, the authors of the study realized that merely analyzing chlorophyll concentrations would require a lengthy period of 30 years to understand the relationship between climate change and the proliferation of phytoplankton. Natural variations in pigment concentrations and photosynthetic organisms could potentially skew the analysis as they aren't strictly tied to the current climate crisis.
Decoding Two Decades of Ocean Hues
In 2019, Stephanie Dutkiewicz, the co-author of the recent paper, presented another study on this subject. According to her new model, the natural variability in ocean colors is less than that of chlorophyll. Therefore, any change brought on by the climate crisis should be easily discernible against the minor, insignificant, and typical variations in other ocean colors – and this could be achieved in 20 years instead of 30.
Testing Hypotheses with Satellite Surveillance
In the recent research, scientists from MIT put the latter hypothesis to the test with actual data. They analyzed the full color spectrum in images of the oceans captured over 21 years by NASA's Aqua satellite's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. This equipment can detect color changes that are invisible to the human eye. While we might perceive the ocean as "all blue", satellites record a complex combination of electromagnetic waves, including blue, green, and even red light.
Leveraging advanced statistical analysis, the team scrutinized alterations in seven ocean colors recorded by the satellite from 2002 to 2022. This allowed them to differentiate between yearly natural fluctuations and more substantial shifts observable over a 20-year span. A transformation beyond the usual ocean surface color variability started to emerge.
Addressing the question of whether these changes had ties with climate change was straightforward. Dutkiewicz's 2019 model simulated two conditions: one incorporating greenhouse gases and the other without. Under the greenhouse gases inclusion scenario, the model anticipated noticeable shifts in about 50% of the world's ocean surface color within 20 years. This prediction perfectly aligned with the analysis of the real data.
Dutkiewicz encourages everyone to take these findings seriously, stating, "These aren't just model-based predictions of upcoming changes. We're witnessing these alterations in reality; our oceans are indeed transforming."
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