How light pollution speeds up the arrival of spring in cities

3D drone satellite aerial view of Birmingham, England. A US-based researcher has found that, combined with high temperatures, light pollution alters the timing of tree greening in cities. Photo: AFP

In large cities, spring comes earlier than in rural areas. The reason? Temperatures are higher there because of pollution, but also because of artificial light. This discovery was made by researcher Lin Meng, winner of the Science & SciLifeLab 2021 prize for young scientists.

Published in the journal Science, her work looks at large cities in the United States and assesses the impact of temperature change and light on the regular day-night cycle on which plants depend.

The researcher particularly focused on artificial light, whose impact on urban vegetation is often overlooked when developing outdoor lighting strategies (streetlights, buildings, advertising displays, etc).

"We as ecologists know a lot about the impact of warming and increased carbon dioxide concentration on plants because these are the two most significant aspects of climate change... The effect of light pollution on vegetation phenology is a blind spot," explains Lin, a postdoctoral scholar at Lawrence Berkeley National Lab in Berkeley, California.

It has long been known that air pollution contributes to the warming of cities, sometimes with a 3°C difference between urban and rural areas. Known as "the urban heat island effect", this phenomenon contributes to altering the seasonal cycles of plants. In the spring, leaf-greening on trees occurs on average six days earlier than in the countryside.

And light pollution may be contributing even more to these differences. Lin found in her study of US cities that artificial light may have advanced the arrival of spring by nine days in areas where artificial light is particularly intense.

Lin hopes to continue her research to determine the specific effect of artificial light sources (LEDs, sodium lamps, etc) on different plant species, as well as to identify a critical period when trees may be particularly sensitive to these lights.

"Answers to these questions will inform decision-making on what types of light we need for different locations to minimise ecological consequences," projected Lin.

"Understanding how city-induced temperature and light influence vegetation both increases our knowledge of these basic ecological interactions and will help us design more resilient urban landscapes," noted Sacha Vignieri, deputy editor in chief of research at Science. – AFP Relaxnews