Anthropogenic changes in the surface all-sky UV-B radiation through 1850-2005 simulated by an Earth system model

by S. Watanabe, T. Takemura, K. Sudo, T. Yokohata, H. Kawase
Atmospheric Chemistry and Physics ()
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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. Re-sponses of UV-B dose to anthropogenic changes in ozone and aerosols are separately evaluated using a series of historical simulations including/excluding these changes. 5 Increases in these air pollutants cause reductions in UV-B transmittance, which oc-cur 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 concentra-tion in the extratropical upper troposphere and lower stratosphere. These transient 10 changes work to decrease the amount of UV-B reaching the Earth's surface, coun-teracting the well-known effect increasing UV-B due to stratospheric ozone depletion, which developed rapidly after ca. 1980. As a consequence, the surface all-sky 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 15 changes to the UV-B change, the transient change in ozone absorption of UV-B mainly determines the total change in the surface all-sky 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 20 the total UV-B change.

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