2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/9132It is likely that one or more gamma-ray bursts within our galaxy have strongly irradiated the Earth in the last Gy. This produces significant atmospheric ionization and dissociation, resulting in ozone depletion and DNA-damaging ultraviolet solar flux reaching the surface for up to a decade. Here we show the first detailed computation of two other significant effects. Visible opacity of NO2 is sufficient to reduce solar energy at the surface up to a few percent, with the greatest effect at the poles, which may be sufficient to initiate glaciation. Rainout of dilute nitric acid is could have been important for a burst nearer than our conservative nearest burst. These results support the hypothesis that the characteristics of the late Ordovician mass extinction are consistent with GRB initiation.12 pages, 2 figures, in press at Geophysical Research Letters. Minor revisions, including details on falsifying the hypothesisAstrophysicsAtmospheric and Oceanic PhysicsGeophysicsSpace PhysicsPopulations and Evolutiontext