Abstract
Abstract. The historical anthropogenic change in the surface all-sky UV-B (solar ultraviolet: 280–315 nm) radiation through 1850–2005 is evaluated using an Earth system model. Responses of UV-B dose to anthropogenic changes in ozone and aerosols are separately evaluated using a series of historical simulations including/excluding these changes. Increases in these air pollutants cause reductions in UV-B transmittance, which occur gradually/rapidly before/after 1950 in and downwind of industrial and deforestation regions. Furthermore, changes in ozone transport in the lower stratosphere, which is induced by increasing greenhouse gas concentrations, increase ozone concentration in the extratropical upper troposphere and lower stratosphere. These transient changes work to decrease the amount of UV-B reaching the Earth's surface, counteracting the well-known effect increasing UV-B due to stratospheric ozone depletion, which developed rapidly after ca. 1980. As a consequence, the surface UV-B radiation change between 1850 and 2000 is negative in the tropics and NH extratropics and positive in the SH extratropics. Comparing the contributions of ozone and aerosol changes to the UV-B change, the transient change in ozone absorption of UV-B mainly determines the total change in the surface UV-B radiation at most locations. On the other hand, the aerosol direct and indirect effects on UV-B play an equally important role to that of ozone in the NH mid-latitudes and tropics. A typical example is East Asia (25° N–60° N and 120° E–150° E), where the effect of aerosols (ca. 70%) dominates the total UV-B change.
Highlights
Excessive solar ultraviolet (UV) radiation reaching the Earth’s surface is known to damage animals and plants living on the ground, as well as those living in the water near the surface (see WMO (2007), WMO (2011), UNEP (2006), UNEP (2010) and references therein)
The net downward flux of solar UV-B radiation is strongly reduced in the troposphere due to: (1) Rayleigh scattering by air molecules whose strength rapidly increases with increasing atmospheric density and with decreasing wavelength of light; (2) scattering by cloud droplets, ice crystals, and precipitating materials; (3) scattering and absorption by natural and anthropogenic aerosols; and (4) absorption by tropospheric ozone whose effect can be enhanced by multiple scattering due to the aforementioned scattering processes in the atmosphere
The historical anthropogenic changes in the surface allsky UV-B radiation through 1850–2005 are evaluated by analyzing the CMIP5 transient historical simulations performed with MIROC-Earth system model (ESM)-CHEM
Summary
Excessive solar ultraviolet (UV) radiation reaching the Earth’s surface is known to damage animals and plants living on the ground, as well as those living in the water near the surface (see WMO (2007), WMO (2011), UNEP (2006), UNEP (2010) and references therein). UV-B radiation sterilizes the surface environment, for example, through exposure of bacilli that float in the atmosphere or live on the ground surface. Ozone in the stratosphere effectively absorbs UV-B radiation and protects animals and plants on the Earth’s surface. The net downward (direct and diffuse) flux of solar UV-B radiation is strongly reduced in the troposphere due to: (1) Rayleigh scattering by air molecules whose strength rapidly increases with increasing atmospheric density and with decreasing wavelength of light; (2) scattering by cloud droplets, ice crystals, and precipitating materials; (3) scattering and absorption by natural and anthropogenic aerosols; and (4) absorption by tropospheric ozone whose effect can be enhanced by multiple scattering due to the aforementioned scattering processes in the atmosphere.
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