Projeções globais de fluxos de radiação UV para o século XXI: avaliações sob presença de aerossóis e nuvens

Abstract

Ozone, aerosols, and clouds influence the ultraviolet radiation (UVR) that reaches the earth’s surface. This study aims to evaluate UVR throughout the 21st century considering the total ozone content (TOC), the total cloud cover (TCC), and the aerosol optical depth at 550 nm (AOD550). For that, I first evaluated current climate (1980 - 2014) simulations provided by six Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) by contrasting them with the fifth generation of European Reanalysis (ERA5) and the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). For future projections, the Shared Socioeconomic Pathways (SSPs; SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) and four time-slices throughout the century (2021 - 2040, 2041 - 2060, 2061 - 2080 and 2081 - 2100) were considered. I used the UVBoost estimator to calculate UV irradiance. Then, the Ultraviolet Index (UVI) at solar noon, daily doses, and exposure times for erythema (Dery and tery) and vitamin D synthesis (DvitD and tvitD) for phototype III were computed. The cloud attenuation factor (𝑓𝐶) was used to analyze the cloud cover impact on UVR projections. As expected, the multi-model mean ensemble from six ESMs showed smaller biases and root-mean-square errors (RMSE) which indicated that the simulations are close to the reanalysis data. For TOC, pronounced increases were projected at mid and high latitudes, towards the end of the century, and under higher radiative forcing scenarios (SSP3-7.0 and SSP5-8.5). Over Antarctica, increases of up to 30.0% projected for 2081 - 2100 indicate ozone recovery. On the other hand, greenhouse gas (GHG) emissions impact the signal of change in the tropical region, with decreases (up to 4.0%) under SSP1-2.6 and increases (up to 7.0%) under SSP3-7.0. Regarding TCC, increases over the Eastern Tropical Pacific Ocean in all SSPs, with maximum values ~27.0% (in the long-term; 2081 - 2100), are related to the Intertropical Convergence Zone (ITCZ). By contrast, the TCC decline in North Africa (up to 21.0%) and South America (up to 16.0%) are consistent with the intensification of subtropical anticyclones. For AOD550, increases of up to 28.0% (SSP3-7.0) and 99.0% (SSP5-8.5) were projected in India, Central, and East Africa at the end of the century (2081 - 2100). On the other hand, decreases in North America, Europe, and China over the century may be due to the air quality policies and pollutant emissions control, mainly under SSP1-2.6. In December, UVI, Dery, and DvitD projected changes were pronounced at mid and high latitudes in the Southern Hemisphere (SH), towards the end of the century and under higher radiative forcing scenarios (SSP3-7.0 and SSP5-8.5). In South America, Australia, and southern Africa, 10 to 20 minutes of exposure at solar noon can induce erythema in phototype III. In contrast, there is no UVR sufficient for vitamin D synthesis at solar noon throughout the century in the United States, Canada, Russia, and Europe. In June, despite the discrepancy in the sign of the projected change between the SSPs, the UVI and Dery were high (UVI ≥ 11; Dery ~ 6.0 kJ m-2) in areas with high population density such as China, India, the Middle East, and the United States. On the other hand, there is no vitamin D synthesis over the century for the scenarios in southern Argentina, southern Chile, and Antarctica. Cloud cover impacts UVI and DvitD more strongly. However, spatial patterns throughout the century have not changed. TCC attenuation can reduce up to 3.5 UVI under scenarios SSP1-2.6 and SSP2-4.5 in South America and part of Central America but still indicate high levels (UVI between 8 and 10). Furthermore, in December and under SSP1-2.6, there were projected attenuations between 1.5 and 1.8 kJ m-2 for Dery and between 2.5 and 3.0 kJ m-2 for DvitD. The results showed that climate change can significantly impact UVR throughout the 21st century and affect human health.