Every change we introduce into the environment, whether small or large, is destined to alter its balance, with effects that are often difficult to predict. This is the case of light pollution, the modern craze for illuminating urban environments like daylight even at night. A phenomenon that has made stars disappear from city skies, makes astronomical observations increasingly difficult even in the most remote and isolated observatories, and which influences the circadian rhythm of humans, animals and plants. Not only that, because new research from the University of Cranfield reveals a new danger linked to artificial lighting at night: it would in fact upset the vital rhythm of plants, increasing the production of CO2 nocturnal without increasing the quantity sequestered during photosynthesis. Thus transforming the role of vegetables in the fight against global warming: no longer a solution, but part of the problem.
Plant metabolism
Let’s start with a minimal review. Plant metabolism is composed of two main processes: photosynthesis and respiration. The first is the mechanism by which plants produce and accumulate energy, in the form of sugars, using solar energy and carbon dioxide to obtain glucose and oxygen. The second, the process through which they transform sugar reserves into energy with which to fuel their cellular processes, using oxygen and obtaining Atp (the fuel of the cells) and carbon dioxide.
The bottom line is that with photosynthesis, plants remove CO2 from the atmosphere, and fix carbon by building trunks, leaves and roots. While in cellular respiration the production of Atp leads to the creation of new CO2. As a rule, photosynthesis prevails during the day, when sunlight is available, and respiration during the night. And the balance between these two processes is positive: plants sequester more carbon dioxide than they release by breathing, and therefore greater plant growth translates into a lower quantity of CO2 in the atmosphere, a lower greenhouse effect, and therefore a lower increase in global temperatures. With the hand of man, however, even this delicate balance now seems to be altered.
The research
The new study, published in the journal Nature climate changeused data collected from 86 carbon flux monitoring stations located in Europe and North America, integrated with satellite observations, to analyze how artificial lighting affects the carbon balance of the plant world. And the results demonstrate that the effects are evident, and negative: night lighting actually increases breathing and the consequent emission of CO2without the plants catching up during the day by increasing photosynthesis.
In short, where the night is illuminated by our artificial lights, plants become net emitters of carbon dioxide, an additional source of climate-altering emissions. “Artificial light is one of the most visible human-caused environmental changes, but its effects often remain hidden,” explains study coordinator Alice Johnston, professor of Environmental Data Science at Cranfield. “It is a widespread problem almost everywhere, which is changing the functioning of ecosystems, altering energy flows, animal behavior, habitats and natural cycles”. To put it simply, brighter nights mean more carbon emissions, and that’s bad news for our planet.
What to do?
Currently, a quarter of the landmass experiences some level of light pollution, and the intensity and prevalence of artificial nighttime lighting is increasing by two percent each year. Enough to have a non-negligible impact on global warming. For this reason, the authors of the research believe that the effects of light pollution on CO emissions2 plants should be taken into consideration in climate models, which is not currently done.
The positive aspect is that unlike greenhouse gas emissions from human activities, plant emissions can be solved with relative ease: turn off the lights, and the problem disappears. “Unlike climate change, it is possible to reduce light pollution literally overnight, with better urban lighting planning,” concludes Johnston. “Using dimmable, directional, and spectrally sensitive lighting technologies is an improvement that can be achieved immediately. And given that lighting accounts for 15 percent of global electricity consumption, and a growing body of research links excessive exposure to lights at night to adverse human health effects, solving the problem of nighttime pollution would be a win-win scenario for the environment, improved energy efficiency, and for health.”