Lighting trends reveal state of the dark sky cloak: light at night and its ecological impacts in Aotearoa New Zealand

Abstract

Artificial light at night (ALAN) exposes many organisms to increased night-time radiance and disrupts natural cycles that have cued the physiology and ecology of plants and animals throughout their evolutionary history. Here, we use satellite data to quantify spatiotemporal trends of ALAN in Aotearoa New Zealand between 2012-2021 and review the literature of the ecological impacts of ALAN. Our results show that the night-time light environment is changing rapidly in Aotearoa New Zealand: while the vast majority (95.2%) of the country had no direct emissions of ALAN, the lit surface area increased by 37.4% (from 3.0% to 4.2%) between 2012 and 2021. A total of 4694 km 2 of the country experienced increased brightness (median increase of 87%) over the decade. In contrast, 886 km 2 became less bright (median decrease 33%), mainly in urban centres where absolute brightness remains high. Our estimated increases in ALAN extent and brightness are underestimates as satellite imagery does not capture sky glow, nor the full extent of the light spectrum emitted by increasingly common light emitting diodes. Impacts of ALAN on the flora and fauna of Aotearoa New Zealand were identified from 39 pieces of literature, with most focussing on behavioural responses in avifauna, mammals, and insects. ALAN is an understudied environmental pollutant, as > 31% of the records described general observations rather than experimental or observational studies and literature describing impacts on groups including herpetofauna and marine mammals was absent, as were studies quantifying impacts on population size, species interactions, or ecosystem functions. At ALAN's current rate of increase, Aotearoa New Zealand is in danger of losing its cloak of darkness, resulting in increased negative environmental impacts. Greater awareness and targeted ecological research are proposed to stimulate change towards minimising ALAN and mitigating the impacts of light emitted into the nocturnal environment. Additional information and declarationsAuthor contributions: EC conceived the idea and conducted the data analysis. EC and BF developed the idea and wrote the manuscript. Data and code availability:The night-time satellite data used in this paper is freely available online, as described in the Methods section. Code is available from the authors upon request.Ethics: The research did not require ethics approval, as it uses existing data and literature.