Like clockwork, humans complain about the lack of sunshine as the winter months draw near. Some scientists, however, think we should be more concerned about the dearth of darkness. Night as we know it is dying, an international team of scientists said in a teleconference on Tuesday, as they discussed their research on the huge increases in light pollution around the world since 2012.

The concept of light pollution isn’t anything new, but we normally only think about it in relation to celestial events we want to see in the night sky, like meteor showers or passing comets. In the teleconference, the scientists, who published a study related to this work in Science Advances on Wednesday, pointed out that it’s time to start thinking about the disruptive effects of all that artificial light on the natural world around us.

“Since the first emergence of life, the biological world is organized to a large extent by natural cycles of variation in light,” said Leibniz Institute of Freshwater Ecology and Inland Fisheries scientist Franz Hölker, Ph.D., a co-author of the new study.

“From an evolutionary perspective now, artificial light at night is a very new stressor.”

This is a graph of changes in artificially lit surface of Earth at night.

In the study, which used data gathered using the Visible Infrared Imaging Radiometer (VIIRS), the researchers found that there are increasingly more regions of the Earth that are lit with artificial light. The VIIRS data, collected as the satellite circled the Earth from pole to pole 14 times a day, showed that, between 2012 and 2016 the size of Earth’s artificially lit region grew at a rate of 2.2 percent per year.

Some countries got more lit than others. In most of the countries in South America, Africa, and Asia, radiance grew, whereas it stayed constant in the United States and Spain, countries previously labeled the Earth’s brightest. The only countries that showed decreases in radiance were Syria and Yemen, which the researchers pointed out are experiencing warfare.

This map from an unrelated study shows North America's artificial sky brightness as a ratio to the natural sky brightness.

The researchers are concerned that, if the increase in global radiance continues to grow at these rates, that it will have serious effects on the Earth’s ecology — and perhaps even on human biology.

“The problem is that light has been introduced in places, times and intensities at which it does not naturally occur and many organisms, there is no chance to adapt to this new stressor,” said Hölker. “As a consequence, natural light cycles have been fundamentally disrupted by the introduction of artificial light into the nighttime environment.”

Hölker points out that the loss of night could disrupt animal “night habits,” which include reproduction or migration patterns. In the plant kingdom, it could cause trees to lose their leaves later than normal or extend their growing periods to abnormal lengths.

In many ways, humans are already experiencing disruptions to their own natural sleep cycles because of their exposure to blue light from the LED lights in smartphones, TVs, and other screens. Blue light is thought to disrupt the production of melatonin, the hormone the body produces to tell the body to go to sleep. At least part of the “loss of night,” the researchers point out, is due to an increase in the use of LEDs, which “has the most biological consequences,” said co-author and National Oceanic and Atmospheric Adminstration scientist Chris Elvidge, Ph.D., in the teleconference. The VIIRS sensors don’t even pick up on blue light, the researchers point out, suggesting that the increases in radiance reported in the study are even greater with respect to human sight.

“Of course if you experience blue light in the night, for instance, then you risk that animals — mammals, especially, and humans — experience this light as physiological day,” said Hölker. “And this is of course a problem.”