DOI: 10.5061/dryad.cfxpnvx23
title: Assessing the effects of artificial light at night on biodiversity across latitude – Current knowledge gaps

description: Aim: Exposure to artificial light at night (ALAN) is a risk factor for
 organisms. Considering the spread and increasing intensity of night
 brightness across the globe, and the key role of light at all biological
 levels, alterations of ecosystems are expected. Yet, we cannot predict the
 severity of the effects of ALAN in several biomes because little
 information is available outside the temperate zone. We reviewed current
 knowledge and identified traits that could be targeted to fill this
 knowledge gap in order to contribute to the elaboration of a
 biogeographical framework for the study of ALAN at the global scale.
 Location: global. Time period: current and next decades. Method: We
 analysed the latitudinal variation of ALAN and focused on environmental
 factors that vary with latitude but that have been overlooked. We reviewed
 biological traits that exhibit latitudinal variation and depend on light
 and photoperiod and compiled information about the predicted changes of
 human demography and road networks across different world regions.
 Results:  Cloud cover amplifies ALAN far away from urbanized
 areas. Because of the higher frequency of overcast sky nights, exposure
 effects may be stronger both at high latitudes and across a large fraction
 of the intertropical zone, though at different times of the year.
 Intertropical biomes host the largest fraction of global biodiversity.
 Although currently they are not the most exposed to ALAN, their human
 populations are growing, and urbanized areas and road networks are
 expanding. Hence, ALAN could have strong ecological consequences, with
 cloud cover as an aggravating factor. Perspectives:  Knowledge
 gaps currently limit our ability to predict the effects of ALAN in
 different biomes. Therefore, it will be important to start investigating
 the consequences of this novel environmental factor across the globe, in
 order to develop a relevant theoretical framework.
description: This is mainly a review and perspective paper but we used already
 published data on the intensity of artificial light at night, cloud cover,
 time of twilight, and human demography. Light and cloud cover data were
 provided with permission from authors. The others were free of
 use. <strong>Artificial light at
 night </strong>- from Falchi, F., Cinzano, P., Duriscoe,
 D., Kyba, C. C. M., Elvidge, C. D., Baugh, K., … Furgoni, R. (2016). The
 new world atlas of artificial night sky brightness. <i>Science
 Advances</i>, <i>2</i>, e1600377.
 https://doi.org/10.1126/sciadv.1600377 
 <strong>Cloud cover fraction
 </strong>- from the moderate resolution imaging spectroradiometer
 (MODIS) mission and provided by the Giovanni online data system, developed
 and maintained by the NASA Goddard Earth Sciences Data and
 Information Services
 Center. https://giovanni.gsfc.nasa.gov/giovanni/ 
 <strong>Twilight</strong> - from
 https://www.esrl.noaa.gov/gmd/grad/solcalc/ and
 https://earthsky.org/?p=235797 &gt; Time of dusk and dawn for
 each month of the year were tabulated for three towns at three latitudes
 and graphs created using R 
 <strong>Human demography</strong> - from United Nations
 Department of Economic and Social Affairs Population Division. (2017).
 World population. Retrieved from
 https://population.un.org/wpp/Publications/Files/WPP20
 17_Wallchart.pdf &gt; Data were mapped using
 QGIS with no transformation.
description: File: <strong>Data Dryad-latitudinal variation in ALAN
 cloud cover</strong> Latitudinal distribution of
 artificial light at night (ALAN) and cloud cover fraction and their
 standard deviations were measured from satellite images and data were
 binned in 5° categories using QGIS. Only terrestrial areas have been
 included in the analysis. Seas and large lakes have been
 excluded. median_latitude: median position of the
 5°latitudinal band alan_count and cloud_count: number
 of pixels with a value alan_sum and cloud_sum: sum of
 values for all counted pixels of the latitudinal band 
 alan_mean and cloud_mean: mean value for each latitudinal band
 computed as sum / count alan_sd and cloud_sd: standard
 deviation for each latitudinal band File:
 <strong>Data Dryad-Daylength and ALAN</strong>
 The table provides the geographical coordinates of three towns
 (Reykavik, Vladivostok and Lagos) as well as the time of sunset and
 sunrise and the duration of twilight at these three locations. Values are
 reported for three definition of twilight: civil twilight (sun declination
 between 0 and 6° below the horizon), nautical twilight (declination
 6–12°), astronomical twilight (declination 12–18°).