Increasing Surface UV Radiation in the Tropics and Northern Mid-Latitudes due to Ozone Depletion after 2010

Excessive exposure to ultraviolet (UV) radiation harms humans and ecosystems. The level of surface UV radiation had increased due to declines in stratospheric ozone in the late 1970s in response to emissions of chlorofluorocarbons. Following the implementation of the Montreal Protocol, the stratospheric loading of chlorine/bromine peaked in the late 1990s and then decreased; subsequently, stratospheric ozone and surface UV radiation would be expected to recover and decrease, respectively. Here, we show, based on multiple data sources, that the May–September surface UV radiation in the tropics and Northern Hemisphere mid-latitudes has undergone a statistically significant increasing trend about 60.0 J m^–2 (10 yr)^–1 at the 2σ level for the period 2010–20, due to the onset of total column ozone (TCO) depletion about −3.5 DU (10 yr)^–1. Further analysis shows that the declines in stratospheric ozone after 2010 could be related to an increase in stratospheric nitrogen oxides due to increasing emissions of the source gas nitrous oxide (N₂O).