Yellowstone National Park’s most famous hot spring, Grand Prismatic, has a vivid blue center surrounded by bands of green, yellow and rusty orange. Multilayered sheets of microorganisms, called “microbial mats,” give the bands their distinctive colors that tend to change slightly with the seasons.
Our world is a colorful place. Just think of the vivid blues, greens, oranges, reds and yellows of Grand Prismatic Spring in Yellowstone National Park, the rainbow-hued mountains of Zhangye National Geopark in China or the shimmering green and purple bands of light in the aurora borealis above the tundra in Churchill, Manitoba, Canada.
In fact, color defines our planet. Earth is known as “The Blue Marble” because of a photograph taken of our home in the cosmos by the crew of the final Apollo mission on December 7, 1972. But that quintessential ocean color has changed significantly in the past 20 years, and the trend is likely a consequence of human-induced climate change.
Parts of the icy “Great White Continent” are changing color, too. Antarctica is shifting from white to green. Gripped by extreme heat events, Antarctica’s plant life is growing at an alarming rate, sparking concerns about how this changing landscape will affect us all.
Such color changes on Earth aren’t unprecedented, however. A long time ago, the planet may have looked very purple.
The rainbow-hued mountains in China’s Zhangye National Geopark look like the work of an artist’s brush. Part of a UNESCO World Heritage site, this stunning formation was created by natural erosion, when layers of iron, minerals, sand and silt blended together to create a kaleidoscope of colors.
Oceans are getting greener due to climate change
You may not have noticed it, but over the past two decades, the color of the world’s oceans has been dramatically changing. The shift from blue to green—though subtle to the human eye—has occurred over 56% of the planet’s oceans, an expanse that is larger than the total land area on Earth.
In a study appearing in the science journal Nature in July 2023, researchers at the Massachusetts Institute of Technology, the National Oceanography Center in the United Kingdom and elsewhere write that the detected changes in ocean color cannot be explained by natural, year-to-year variability alone. While it’s not yet possible to say exactly how marine ecosystems are changing so that they reflect the shifting color, the scientists are pretty sure of one thing: human-induced climate change is likely the driver.
In particular, the tropical ocean regions near the equator have become steadily greener over time. The ocean’s color is a visual product of whatever lies within its upper layers. Generally, waters that are deep blue reflect very little life, whereas greener waters indicate the presence of phytoplankton—plantlike microbes that are abundant in the upper ocean and that contain the green pigment chlorophyll. The pigment helps plankton harvest sunlight, which they use to capture carbon dioxide from the atmosphere and convert it into sugars.
The frightening shift in ocean color from blue to green indicates that ecosystems within the ocean’s surface must also be changing, since the color of the ocean is a reflection of the materials and organisms in its waters.
Phytoplankton are the foundation of the marine food web that sustains progressively more complex organisms, on up to krill, fish, and seabirds and marine mammals. Phytoplankton are also a powerful muscle in the ocean’s ability to capture and store carbon dioxide. Scientists are, therefore, keen to monitor phytoplankton across ocean surfaces to learn how these essential communities might respond to climate change. To do so, they’ve tracked changes in chlorophyll, based on the ratio of how much blue versus green light is reflected from the ocean surface, which can be monitored from space.
But around a decade ago, another study showed that if scientists were tracking chlorophyll alone, it would take at least 30 years of continuous monitoring to detect any trend that was driven specifically by climate change. The reason is that the large, natural variations in chlorophyll from year to year would overwhelm any anthropogenic influence on chlorophyll concentrations. It follows, then, that it would take several decades to pick out a meaningful, climate-change-driven signal amid the normal noise.
But in 2019, the results of a separate paper showed through a new model that the natural variation in other ocean colors is much smaller compared to that of chlorophyll. Therefore, any signal of climate-change-driven changes should be easier to detect over the smaller, normal variations of other ocean colors. It was predicted that such changes should be apparent within 20, rather than 30, years of monitoring.
The differences in ocean colors that satellites pick up are sometimes too subtle for human eyes. To us, much of the water may appear blue, whereas the true color may contain a mix of subtler wavelengths, from blue to green and even red.
So, for the study published in Nature in July 2023, the whole spectrum of the ocean’s colors was looked at rather than just those in chlorophyll alone. Measurements of ocean color taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite were analyzed. MODIS, which has been monitoring ocean color for 21 years, takes measurements in seven visible wavelengths, including the two colors researchers traditionally use to estimate chlorophyll.
The differences in color that the satellite picks up are too subtle for human eyes to differentiate. Much of the ocean appears blue to our eyes, whereas the true color may contain a mix of subtler wavelengths, from blue to green and even red.
The scientists carried out a statistical analysis using all seven ocean colors measured by the satellite from 2002 to 2022. First, they looked at how much the seven colors changed from region to region during a given year, which gave them an idea of their natural variations. They then zoomed out to see how these annual variations in ocean color changed over a longer, two-decade stretch. This analysis turned up a clear trend, above the normal year-to-year variability.
Monitoring ocean colors beyond chlorophyll could give scientists a clearer, faster way to detect climate-change-driven shifts in marine ecosystems. Color alterations reflect changes in plankton communities, and that will impact everything that feeds on plankton.
To see whether this trend is related to climate change, the researchers looked to the model from 2019. This model simulated the Earth’s oceans under two scenarios: one with the addition of greenhouse gases, and the other without it. The greenhouse-gas model predicted that a significant trend should show up within 20 years and that this trend should cause changes to ocean color in about 50% of the world’s surface oceans—almost exactly what the Nature paper’s authors found in their analysis of real-world satellite data. This suggests that the observed trends are not a random variation in the Earth’s system but are consistent with anthropogenic climate change.
These results show that monitoring ocean colors beyond chlorophyll could give scientists a clearer, faster way to detect climate-change-driven alterations to marine ecosystems. Changes in color reflect modifications in plankton communities, and that will impact everything that feeds on plankton. It will also affect how much carbon the ocean will take up, because different types of plankton have varying abilities to do so.
This gives additional evidence of how humans are affecting life on Earth over vast areas; in fact, over the whole biosphere.
The Antarctic Peninsula is a long mountain chain that points north to the tip of South America. Off the west coast of the peninsula is the Lemaire Channel, shown here. This part of Antarctica has been warming five times faster than the global average.
Antarctica is getting greener as seen from space
The world’s oceans aren’t the only thing turning green.
In a brand-new report published in the journal Nature Geoscience in October 2024, scientists used satellite data and imagery to analyze vegetation levels on the Antarctic Peninsula, a long mountain chain that points north to the tip of South America and which has been warming much faster than the global average.
They found that plant life—mostly mosses—had increased in this harsh environment more than 10-fold over the past four decades. Vegetation covered less than 0.4 square miles of the Antarctic Peninsula in 1986 but had reached almost five square miles by 2021. The rate at which the region has been greening over nearly four decades has also been speeding up, accelerating by more than 30% between 2016 and 2021.
The more the Antarctic Peninsula greens, the more soil will form and the more likely the region will become more favorable for invasive species, potentially threatening native wildlife, such as these emperor penguins.
While the landscape is still almost entirely ice, rock and snow, this small, green area has grown exponentially since the mid 1980s. And these effects are visible from space. There could be even more vegetation than identified, since the methods used by scientists mainly detect larger, greener moss fields. But there are also substantial areas of lichens, grass, and green and red snow algae that contribute to Antarctica’s expanding vegetation.
Although it’s billed as the coldest place on Earth, Antarctica has recently been gripped by extreme heat events. This summer, parts of the continent experienced a record-breaking heat wave with temperatures climbing up to 50 degrees Fahrenheit above normal from mid-July. In March 2022, temperatures in some regions reached up to 70 degrees above normal, the most extreme temperature departures ever recorded here.
As fossil fuel pollution continues to heat up the world, Antarctica will keep on warming and this greening is only likely to accelerate, the scientists predict. The more the peninsula greens, the more soil will form and the more likely it will become more favorable for invasive species, potentially threatening native wildlife. Plant fragments, seeds and spores can readily find their way to the Antarctic Peninsula on the boots or equipment of researchers and tourists, or via more traditional routes associated with migrating birds and the wind, so the risk is great.
Plant fragments, seeds and spores sometimes find their way to the Antarctic Peninsula via migrating birds, such as this adult Wilson’s storm petrel, sitting on a rock ledge on Half Moon Island in the Antarctic Peninsula region.
The greening could also reduce the peninsula’s ability to reflect solar radiation back into space, because darker surfaces absorb more heat. These impacts would likely only be local, but they could help further accelerate the growth of plant life as the climate continues to warm. The researchers conclude that this iconic landscape could be changed forever and remind us that the influence of anthropogenic climate change has no limit in its reach.
Earth may have been purple in the past
This isn’t the first time that the Earth’s waters and lands have changed their predominant colors, however. The earliest life on Earth might have been just as purple as it is green today.
If you walk outside, chances are you’ll see a lot of green in nature. That’s the result of photosynthesis, the process by which plants convert energy from the sun into useful chemical energy that they need to live while producing oxygen for the rest of us. A key part of this process is the pigment chlorophyll, which absorbs energy from sunlight and uses it to convert carbon dioxide and water into sugars.
Primitive microbes that used retinal to harness the sun’s energy might have dominated early Earth, tinting some of the planet’s first biological hot spots purple. Today, Kealia Pond in Maui, Hawaii, displays retinal in its halobacteria, resulting in a look that may have been common on early Earth.
The authors of some recent NASA-supported research, however, argue that a purple-tinged molecule called retinal likely preceded chlorophyll as the dominant sunlight-absorbing molecule. Retinal, today found in the plum-colored membrane of a photosynthetic microbe called halobacteria, absorbs green light and reflects red and violet light back, the combination of which appears purple. Primitive microbes that used retinal to harness the sun’s energy might have dominated early Earth, thus tinting some of the first biological hot spots on the planet a distinctive purple color. The “Purple Earth” stage would date somewhere between 2.4 to 3.5 billion years ago, prior to the Great Oxygenation Event, which was likely due to the rise of chlorophyll-based photosynthesis.
The biologists speculate that retinal and chlorophyll coevolved together, but that retinal likely came first because it’s a simpler molecule and would have been easier to produce in the low-oxygen environment of early Earth. Being latecomers, microbes that used chlorophyll could not compete directly with those utilizing retinal, but they survived by developing the ability to absorb the very wavelengths retinal did not use. After a while, the researchers say, the balance tipped in favor of chlorophyll because it is more efficient than retinal.
Another interesting aspect of the NASA research is that if Earth had a retinal stage and since retinal is a simpler molecule than chlorophyll, it would be reasonable to consider this when looking for new, inhabitable (or already inhabited) planets. It may be that chlorophyll-based life is the more prominent one; but if you only search for chlorophyll on a planet that is at an early stage of evolution, you might miss the life on it because you’re looking at the wrong wavelength. In fact, it’s entirely possible that retinal-based life could be more widespread throughout the universe.
Expanding industrial activities in marine areas—called “blue acceleration”—has resulted in a rapid decline in marine biodiversity.
“Blue acceleration” is getting a makeover
The good news is that protecting the world’s oceans against accelerating damage from human activities—and keeping them blue—could be cheaper and take up less space than previously thought.
Expanding industrial activities in marine areas beyond national jurisdictions (ABNJs)— such as the high seas and the international seabed beyond exclusive economic zones—has resulted in a rapid decline in marine biodiversity. This “blue acceleration” means that current marine protection methods look at each sector—such as fishing, shipping and deep-sea mining industries—separately, and all these activities have their own suite of impacts on communities, ecosystems and species.
In response, researchers, who published a paper in the journal One Earth in February 2024, assessed the design of different networks of marine protected areas (MPAs) across the Indian Ocean. They investigated the potential trade-offs associated with including multiple stakeholders in a cross-sectoral—as opposed to sector-specific—protected area network for ABNJs in the Indian Ocean.
A new study finds that we can reduce the size of Marine Protected Areas from 25% to 8% while meeting the same conservation objectives. This would still achieve 30% coverage for important biodiversity features, including key life-cycle areas for marine megafauna, such as whales.
First, they created three sector-specific plans—those involving fishing, mining and shipping—to identify optimal locations for strict, no-take MPAs. They then created a cross-sectoral no-take plan that minimizes the opportunity cost to all stakeholders simultaneously, looking at the overall picture with each stakeholder in mind. After generating these plans, they compared the three sector-specific solutions, as well as their sum, to the cross-sectoral solution.
The scientists found that the cross-sectoral approach met the same conservation targets at much lower additional costs for each stakeholder than if all sector-specific plans are implemented without coordination. For example, the fishing sector might lose 20% of its potential revenue under the cross-sectoral plan, but it would lose 54% if all sector-specific plans were implemented concurrently without coordination. This was consistent for the mining and shipping sectors, with the shipping sector now losing 2%, instead of 26% of its potential revenue, and the mining sector now losing 1% instead of close to 8%.
The results also showed that we can reduce the size of MPAs from 25% of the spatial plan to 8% while meeting the same conservation objectives. This would still achieve 30% coverage for important biodiversity features, including key life-cycle areas for marine megafauna, areas of biological and ecological interest, and areas important to deep-sea ecosystems, such as plateaus, seamounts and vents.
The “Blue Marble” is a photograph of Earth taken on December 7, 1972, by either Ron Evans or Harrison Schmitt aboard the Apollo 17 spacecraft on its way to the moon. This view from about 18,268 miles from the Earth’s surface has become one of the most reproduced images in history.
Researchers believe the cross-sectoral approach can be a first step to implementing the conservation objectives of the recently signed United Nations High Seas Treaty. They conclude that, ultimately, the goal is not only to minimize conflicts between conservationists and multiple industries, but also to ensure marine life is protected against the negative impacts from all three industries at once.
Colorful hues and “marble” blue
Our planet and its natural beauty are simply jaw-dropping. From hot springs and deep canyons to mountain meadows and night skies, the planet is filled with awe-inspiring natural wonders bursting with color.
The Apollo 17 image—released during a surge in environmental activism during the 1970s—gave us the collective impression, however, that our home is overwhelmingly blue. So, while the “greening” of our Earth can be a good thing for so many reasons, keeping our planet blue is also a strikingly beautiful aspiration.
Here’s to finding your true places and natural habitats,
Candy
