Widespread influence of artificial light at night on ecosystem metabolism

nature climate change Article https://doi.org/10.1038/s41558-025-02481-0 Widespread influence of artificial light at night on ecosystem metabolism Received: 10 April 2025 Alice S. A. Johnston , Jiyoung Kim & Jim A. Harris Accepted: 8 October 2025 Published online: xx xx xxxx Check for updates Artificial light pollution is increasing worldwide with pervasive effects on ecosystem structure and function, yet its influence on ecosystem metabolism remains largely unknown. Here we combine artificial light at night (ALAN) intensity metrics with eddy covariance observations across 86 sites in North America and Europe to show that ALAN indirectly decreases annual net ecosystem exchange by enhancing ecosystem respiration (Re). At half-hourly and daily scales, we detect consistent nonlinear interactions between ALAN and night duration, with Re increasing under higher ALAN and partially decoupling from gross primary production. At the annual scale, gross primary production shows no direct ALAN response and is instead influenced by the growing season length and urban proximity, whereas Re responds more strongly and consistently across timescales. Our findings show that ALAN disrupts the fundamental energetic constraints on ecosystem metabolism, warranting the inclusion of light pollution in global change and carbon–climate feedback assessments. Artificial light pollution is accelerating across the globe1,2 and has widespread consequences for people3,4 and the planet5–7. Shifts in the luminance and spectral composition of the nocturnal environment modify the physiology, behaviour and ecological interactions of organisms7–11, which together play a fundamental role in ecosystem metabolism12,13. Ecosystem metabolism, comprising gross primary production (GPP) and ecosystem respiration (Re), directs the magnitude and direction of carbon–climate feedbacks via net ecosystem exchange (NEE)14. Around one quarter of global terrestrial ecosystems are exposed to artificial light at night (ALAN)15, but the effects on ecosystem metabolism are currently unknown. Changing daily and seasonal cycles of light and dark10 could decouple the timing of biological processes across trophic networks16. Trophic groups are also exposed to ALAN at different intensities and have varying sensitivities to luminance and spectral composition17. Plant responses to photoperiod are influenced even at low ALAN intensities18,19, and longer-term exposure influences seasonal phenology, growth form, resource allocation and, thus, potentially carbon fixation20. High ALAN intensity exposure in urban areas disrupts the behavioural patterns of nocturnally migrating birds21 and plant diversity22 and restructures soil microbial communities, reducing the functional genes involved in nutrient regulation and plant health23. Cranfield Environment Centre, Cranfield University, Cranfield, UK. Nature Climate Change Together, the observed effects of ALAN across levels of biological organization and diverse taxa suggest a potential cascading impact on ecosystem structure and function. Previous studies of ALAN effects, however, have focused on local or experimental manipulations, leaving uncertainty about whether ALAN effects persist at the ecosystem level and longer timescales. GPP and Re are fundamentally constrained by shortwave (solar) radiation (SW) and temperature (T), respectively24–26. That is, SW determines the direction and duration of energy flow between the atmosphere and ecosystems, and T determines the rate of reactions12. Although ALAN is not expected to influence SW or T directly, artificial light could disrupt the processing of energy according to these fundamental constraints via acclimation, compensation and adaptation strategies27,28. A better understanding of the magnitude and direction of ALAN effects on ecosystem metabolism could help constrain carbon– climate processes in Earth system models (ESMs)29. Specifically, largely uncertain ESM processes and their response to climatic factors could be compounded by the chronic effects of pervasive anthropogenic stressors, such as ALAN. Global efforts to measure carbon exchange across diverse ecosystems30 combined with satellite observations of ALAN distribution and intensity across the land surface2,31 enable the exploration of artificial e-mail: Article https://doi.org/10.1038/s41558-025-02481-0 b c Low Medium High 40 Latitude 10 5 36 32 28 0 d Latitude (°) Number of sites a 30 e 35 40 0 f 20 40 60 55 DN <10 (low) DN ≥ 10 < 30 (medium) DN ≥30 (high) 50 6 45 3 0 Latitude (°) Number of sites 9 40 40 45 50 55 Latitude (°) 0 20 40 60 ALAN (DN) Fig. 1 | Distribution of flux tower sites across artificial light intensity in North America and Europe. a,d, The location of 86 eddy covariance flux tower sites from FLUXNET2015 (symbols, colours indicate ALAN intensity according to DN (higher values represent greater luminance of light at night) (as in d) displayed over a harmonized global nighttime light map for 2012 (for visualization only) in North America (n = 34) (a) and Europe (n = 52) (d). b,e, The latitudinal distribution of sites with different ALAN intensities for North America (b) and for Europe (e), in 2° N intervals. c,f, The ALAN intensities of selected FLUXNET2015 sites, averaged across site years (the number of years with observational data per site), for North America (c) and Europe (f) according to DN with symbol size indicating number of site years (range: 1–20 years per site between 1992 and 2014, total site years in c is 211 and in f is 412). Basemaps in a and d were generated with QGIS using the harmonized global nighttime light dataset32 under a Creative Commons license CC BY 4.0. light’s influence on terrestrial ecosystem metabolism. Here, we leverage the harmonized nighttime light dataset of Li et al.32 and eddy covariance observations from FLUXNET201530 to investigate the instantaneous and aggregated influence of ALAN on ecosystem-scale NEE, GPP and Re fluxes. Although both datasets have global coverage, the location of eddy covariance flux towers are biased towards dark sky regions (Extended Data Fig. 1). Following definitions by Li et al.32 and others33, we use three digital number (DN, higher values represent greater luminance of light at night; Methods) groups representative of low (DN <10), medium (DN ≥ 10 < 30) and high (≥30, representative of urban boundaries) ALAN intensity to identify regions with FLUXNET2015 sites across a range of ALAN intensities. North America and Europe were the only regions, globally, with more than one high ALAN intensity FLUXNET2015 site (Methods; Fig. 1a,d). Within both North America and Europe, sites were selected on the basis of latitudinal ranges at which medium or high ALAN intensity sites were present (Fig. 1b,e) to minimize climatic factors in higher or lower latitude sites being ascribed to low ALAN intensities. In total, 86 FLUXNET2015 sites were selected, (...truncated)