Across the planet, scientists are observing ecosystems lose the colours that once defined them.
Coral reefs turn ghost-white during marine heatwaves, their once-fluorescent pinks, greens and blues draining away almost overnight. Vast stretches of ocean have shifted toward deeper, more homogenous blues.
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Forests fade from viridescence to a dusty yellow-brown during drought, distinct from the rich reds and golds of autumn. Even the plumage of some birds appears less vibrant.
These changes may seem simply aesthetic, but colour is far more than beauty – especially under heat and atmospheric stress.
Colour as an indicator of health
It is a biological signal, a measure of energy, and, according to researchers in a growing field known as chromatic ecology, a powerful indicator of ecosystem health.
One of the clearest examples of colour loss comes from coral reefs. Their symbiotic algae is responsible for their vivid pigments but due to prolonged heat stress, corals expel this algae, bleaching them white.
In fact, more than half of the world’s coral reefs have experienced this severe bleaching in the past two decades. These events weaken corals and can lead to mass mortality if temperatures remain high
When reefs lose colour, they are also losing function, as they become more vulnerable to disease and struggle to provide the complex shelter that fish, crustaceans and invertebrates depend on.
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Colour shifts are also visible across the entirety of the world’s open oceans. Analysis of two decades of satellite data shows that more than half of the global ocean surface has changed colour as warming alters phytoplankton communities.
These microscopic organisms shape how the sea absorbs and reflects light. As their abundance and composition change, vast regions appear more monochromatic. Though subtle to the human eye, this chromatic shift signals that the base of the marine food web is reorganising under heat stress.
On land, colour loss often begins with drought. Forests and grasslands are green because of chlorophyll, which enables plants to capture carbon and regulate water and energy exchange.
However, “heat and drought raise the atmosphere’s ‘thirst,’ forcing plants to close their stomata,” explains Dr. César Terrer, a terrestrial ecologist at the Massachusetts Institute of Technology, USA.
“This shuts down photosynthesis, chlorophyll breaks down, canopies thin, and at large scales, forests lose their greenness, often an early warning sign of deeper ecological change.”
He notes that the Amazon’s carbon sink has weakened in regions hit by repeated droughts, fires and windstorms.
Colour as communication
We can see colour changes in vertebrate animals as well. In birds, plumage carries vast amounts of information.
“For birds, colour is a communication system,” says Dr. Mary Caswell Stoddard, who specialises in evolutionary biology at Princeton University, USA. “They use it to attract mates, to hide from predators, to deceive rivals and to find food.”
In some species, human-altered habitats appear to dull those signals. Studies of urban songbirds in Europe have found that nestlings growing up in cities show paler, less saturated yellow breast plumage than those in nearby forests, likely because their diets contain fewer carotenoid-rich insects.
As flowering times shift with warming seasons, birds may also lose synchrony with the colour cues they rely on to forage.
In many regions, coral reefs, oceans, forests, birds and meadows all show chromatic shifts as they respond to heat, drought and seasonal disruption.
Yet these changes are not uniformly bleak. Across landscapes and seascapes, colour often returns when stress is reduced and ecosystems are given time to recover.
After California’s prolonged droughts, many forests and grasslands have rapidly regained their greenness following years with stronger rainfall.
Like a world in a storybook emerging from winter to spring, even the dullest natural landscapes can brighten when pressure eases.
Top image: coral bleaching on the Great Barrier Reef in Australia. Credit: Getty
