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Clouds Amplify Ecological Light Pollution

02.03.2011 13:25

The brightness of the nightly sky glow over major cities has been shown to depend strongly on cloud cover.

Publication by Kyba CCM, Ruhtz T, Fischer J, Hölker F (2011) Lunar Skylight Polarization Signal
Polluted by Urban Lighting. Journal of Geophysical Research.

In natural environments, clouds make the night sky darker by blocking the light of the stars. But around urban centers, this effect is completely reversed, according to a new study by a group of physicists and ecologists at the Free University of Berlin (FU) and the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB).

"We found that overcast skies were almost three times brighter than clear at our rural location, and ten times as bright within the city itself," says the lead author of the study, Dr. Christopher Kyba, physicist at the Institute for Space Sciences at the FU. Their research was reported on February TBA, 2011, in the open-access journal PLoS ONE.

"The astronomers who founded the study of light pollution were concerned with how sky glow obscured the stars on perfectly clear nights," says Kyba, "and researchers studying the potential influences of sky glow on human or ecosystem health often cite the results from satellite measurements taken on clear nights. What our study shows is that when considering biological impact on humans and the environment, the amplification of light pollution by clouds is large, and should be taken into account."

The study compares measurements of clear and cloudy sky brightness data taken using "Sky Quality Meters" during five months in the spring and summer of 2010. Two monitoring stations took data at locations 10km and 32km from the center of Berlin. "Recognition of the negative environmental influences of light pollution has come only recently," says Dr. Franz Hölker, ecologist, study author, and project leader of Verlust der Nacht (VdN - Loss of the Night).

"Now that we have developed a software technique to quantify the amplification factor of clouds, the next step is to expand our detection network. The Sky Quality Meter is an inexpensive and easy to operate device, so we hope to recruit other researchers and citizen-scientists from around the world to build a global database of nighttime sky brightness measurements." The authors encourage those interested in participating in such a measurement to contact them at

The research was funded by two interdisciplinary projects, MILIEU and VdN.
An interdisciplinary project of the FU, MILIEU – center for urban earth system studies, was initiated as a focus area at the FU, funded by the German excellence initiative, in order to investigate the bottom-up and top-down interactions between urban agglomerations and the climate and environment.
The VdN project, funded by the German Ministry of Education and Research, is specifically devoted to quantifying light pollution and investigating its impact on humans and the environment.

Funding Statement: This work was supported by the project Verlust der Nacht (funded by the Federal Ministry of Education and Research, Germany, BMBF-033L038A) and by MILIEU (FU Berlin). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Kyba CCM, Ruhtz T, Fischer J, Hölker F (2011) Lunar Skylight Polarization Signal
Polluted by Urban Lighting. Journal of Geophysical Research. doi: 10.1029/2011JD016698

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