Satellite Observations Show Reductions in Light Emissions at International Dark Sky Places During 2012-2020

Abstract

Hyde et al. previously examined the trends in light emission measured by satellite for 98 communities located in or near areas certified as “International Dark Sky Places” (IDSP), and did not find evidence of a difference in trends in comparison to 98 communities of similar size located further away. Here we re-examine the satellite dataset, making use of a newly available correction for the radiance of atmospheric airglow, and extending the analysis period by an additional two years. The new dataset is consistent with the hypothesis that light emissions tend to decrease in communities in or near certified IDSP (median value of -1.6% per year), and is in tension with the hypothesis that there is no difference between these communities and others located further away (median increase of +0.1% per year). While the null hypothesis of no difference in the certified regions still cannot be entirely ruled out (Kolmogorov-Smirnov test probability of 2.5%), it appears likely that IDSP certification is associated with changes in light emissions.