A new study published in Nature Climate Change warns that artificial light at night (ALAN) — from streetlights, billboards, and urban glow — is subtly but significantly disturbing the planet’s natural carbon balance. The research reveals that ALAN increases ecosystem respiration, meaning that the world’s land ecosystems may be releasing more carbon dioxide than previously thought, even without changes in temperature or land use.
The study, conducted by researchers Alice S. A. Johnston, Jiyoung Kim, and Jim A. Harris, analyzed data from 86 observation sites across North America and Europe. Using the FLUXNET2015 eddy‐covariance tower network, the scientists examined how nighttime lighting intensity affects three major indicators of ecosystem metabolism: net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (Rₑ).
“Artificial light at night has become one of the fastest-spreading human-made pollutants on Earth,” said lead author Johnston. “Yet, until now, its influence on how ecosystems breathe — on how they take in and release carbon — has been largely overlooked.”
Effect of ALAN
To understand this phenomenon, the researchers combined high-resolution nighttime light satellite data with long-term ecosystem carbon flux measurements. Sites were classified according to their exposure to ALAN: low, medium, or high, based on luminance levels in digital number (DN) values.
They then applied mixed-effects statistical models and structural equation modeling to detect how light intensity interacts with night duration, temperature, and season length. Data were analyzed at multiple timescales — half-hourly, daily, and yearly — to reveal both short-term fluctuations and long-term trends.
“We wanted to capture both the immediate effects of artificial light during the night and its cumulative impact over the growing season,” explained Kim. “It’s not just about one bright lamp — it’s about how persistent night-time illumination changes the entire rhythm of an ecosystem.”
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Light Pollution
The results show a clear pattern: ecosystems exposed to higher levels of artificial light tend to exhibit stronger respiration activity. In other words, they release more carbon dioxide at night.
However, the effect on gross primary production — the rate at which plants capture carbon through photosynthesis — was less consistent and generally weaker. This imbalance between carbon capture and release means that light-polluted ecosystems may act as smaller carbon sinks or, in some cases, even turn into carbon sources.
At finer time scales, the relationship between ALAN and respiration was nonlinear. During shorter nights, the effect was small, but as night duration increased, respiration rose sharply with higher light intensity. This suggests that artificial light disrupts the natural synchronization between plant photosynthesis and nighttime recovery processes.
“Essentially, ecosystems that should be resting and conserving energy are instead working overtime,” said Harris. “That extra metabolic activity burns through carbon that would otherwise remain stored in plants and soil.”
The structural equation models used in the study confirmed that most of ALAN’s influence on carbon fluxes occurs indirectly — primarily through elevated respiration — rather than through direct suppression of photosynthesis.
This finding points to a critical insight, light pollution may not just affect nocturnal animals or star visibility; it is subtly changing the fundamental energy balance of ecosystems worldwide.
Broader Implications
The study’s authors warn that artificial light could be a hidden driver undermining the effectiveness of global carbon sinks, especially as lighting expands with urbanization. The world’s illuminated areas are growing by about 2–6 percent per year, according to satellite estimates, often without consideration for ecological impacts.
“If ecosystems respire more carbon at night due to lighting, their role in offsetting emissions could be weaker than expected,” Johnston said. “This adds another layer of complexity to how we model climate-carbon interactions.”
The researchers stress that unlike many other environmental stressors, ALAN can be mitigated relatively easily. Solutions include reducing excessive lighting, shielding lamps to minimize skyglow, and using light spectra less disruptive to biological processes — such as warmer, amber-toned LEDs instead of bright white or blue ones.
Environmental experts not involved in the study have also noted its importance. Dr. Elena Pires, an ecologist from the University of Lisbon, commented that “the research shows how something as simple as night lighting can ripple through ecosystems and climate systems in ways we hadn’t fully grasped.”
Not Just Visual Intrusion
Despite its robust data, the authors acknowledge some limitations. The FLUXNET network primarily represents temperate ecosystems with low to moderate light pollution, leaving tropical, arid, and highly urbanized regions underrepresented. They call for more sensors capable of capturing light intensity and spectrum at finer scales, particularly in biodiversity-rich regions like Southeast Asia and the Amazon.
Future studies will need to link ecosystem-scale observations with experimental data — for instance, measuring how soil microbes, roots, and nocturnal insects respond directly to varying light conditions.
Still, the message is clear: artificial light at night is not just a visual intrusion. It is a growing environmental stressor with global consequences. (Wage Erlangga)
