Clear-sky ultraviolet radiation modelling using output from the Chemistry Climate Model Initiative

Abstract

Abstract. We have derived values of the ultraviolet index (UVI) at solar noon using the Tropospheric Ultraviolet Model (TUV) driven by ozone, temperature and aerosol fields from climate simulations of the first phase of the Chemistry-Climate Model Initiative (CCMI-1). Since clouds remain one of the largest uncertainties in climate projections, we simulated only the clear-sky UVI. We compared the modelled UVI climatologies against present-day climatological values of UVI derived from both satellite data (the OMI-Aura OMUVBd product) and ground-based measurements (from the NDACC network). Depending on the region, relative differences between the UVI obtained from CCMI/TUV calculations and the ground-based measurements ranged between −5.9 % and 10.6 %. We then calculated the UVI evolution throughout the 21st century for the four Representative Concentration Pathways (RCPs 2.6, 4.5, 6.0 and 8.5). Compared to 1960s values, we found an average increase in the UVI in 2100 (of 2 %–4 %) in the tropical belt (30∘ N–30∘ S). For the mid-latitudes, we observed a 1.8 % to 3.4 % increase in the Southern Hemisphere for RCPs 2.6, 4.5 and 6.0 and found a 2.3 % decrease in RCP 8.5. Higher increases in UVI are projected in the Northern Hemisphere except for RCP 8.5. At high latitudes, ozone recovery is well identified and induces a complete return of mean UVI levels to 1960 values for RCP 8.5 in the Southern Hemisphere. In the Northern Hemisphere, UVI levels in 2100 are higher by 0.5 % to 5.5 % for RCPs 2.6, 4.5 and 6.0 and they are lower by 7.9 % for RCP 8.5. We analysed the impacts of greenhouse gases (GHGs) and ozone-depleting substances (ODSs) on UVI from 1960 by comparing CCMI sensitivity simulations (1960–2100) with fixed GHGs or ODSs at their respective 1960 levels. As expected with ODS fixed at their 1960 levels, there is no large decrease in ozone levels and consequently no sudden increase in UVI levels. With fixed GHG, we observed a delayed return of ozone to 1960 values, with a corresponding pattern of change observed on UVI, and looking at the UVI difference between 2090s values and 1960s values, we found an 8 % increase in the tropical belt during the summer of each hemisphere. Finally we show that, while in the Southern Hemisphere the UVI is mainly driven by total ozone column, in the Northern Hemisphere both total ozone column and aerosol optical depth drive UVI levels, with aerosol optical depth having twice as much influence on the UVI as total ozone column does.

Effects of Ozone and Clouds on Temporal Variability of Surface UV Radiation and UV Resources over Northern Eurasia Derived from Measurements and Modeling

“…This analysis projects an increase in average Eery of about 2-4% in 2100 in the tropical belt (30 • N-30 • S) and a 1.8% to 3.4% increase in the midlatitudes in the Southern Hemisphere for RCP (Representative Concentration Pathway) 2.6, 4.5 and 6.0, compared to 1960s, which partly contradict to the results obtained in [35]. The projected increase in Eery reported in [37] results from the assumption that the atmospheric aerosol loading will decrease greatly over the course of the 21st century, which is debatable. The analysis of erythemal radiation according to the CCMI simulations [2] projects Eery to decrease by 5-15% in the northern hemisphere during summer and autumn mainly due to ozone recovery in 2085-2095 compared with 2010-2020 according to the RCP 6.0 scenario.…”

“…The INM-RSHU CCM, as many other CCM models (see, for example, discussion in [37]), did not reproduce an observed significant positive change in CMFuv during the last decades, which can reach up to 4-8% per decade, according to the ERA-Interim dataset over several areas in Northern Eurasia.…”

“…Using this approach, the effects of various factors on future UV variations were estimated. Chemistry-climate models (CCMs) have also been used for estimating changes in UV radiation in the past and future [9,11,[35][36][37][38]. In [35] the projections of erythemal irradiance from 1960 to 2100 have been made using radiative transfer calculations and projections of ozone, temperature and cloud change from 14 CCM, as part of the CCMVal-2 activity of SPARC (Stratosphere-troposphere Processes And their Role in Climate) project.…”

“…In Ref. [37] the analysis of Eery variations has been made by using the clear-sky data from the first phase of the Chemistry-Climate Model Initiative (CCMI) as input to the TUV (Tropospheric Ultraviolet and Visible) radiation model. This analysis projects an increase in average Eery of about 2-4% in 2100 in the tropical belt (30 • N-30 • S) and a 1.8% to 3.4% increase in the midlatitudes in the Southern Hemisphere for RCP (Representative Concentration Pathway) 2.6, 4.5 and 6.0, compared to 1960s, which partly contradict to the results obtained in [35].…”

Solar UV Irradiance in a Changing Climate: Trends in Europe and the Significance of Spectral Monitoring in Italy

“…Uncertainties about the future rate of ozone recovery arise from the recent unexpected emissions of anthropogenic ODS already controlled by the Montreal protocol, as well as emissions of ODS, which have not yet been forbidden [68,69]. Climate change-induced alterations of stratospheric temperatures and circulation patterns are also expected to have a significant impact on the future levels and spatial distribution of stratospheric ozone [70][71][72][73], which in turn would affect solar UV radiation [74][75][76][77][78][79].…”