The impact of a potential future grand solar minimum on biological health effects : erythema, DNA damage and vitamin D production

Abstract

Ultraviolet radiation (UVR) emitted by the Sun causes both beneficial and harmful biological responses in humans that are essential for skin and musculoskeletal health. Solar UVR also regulates stratospheric ozone production, which in turn limits UVR transfer to the Earth’s surface. This thesis aims to improve the understanding of the relationship between solar activity and biological responses by investigating the impact of a potential 21st century grand solar minimum on three biological health effects: erythema, DNA damage, and vitamin D production. Using the libRadtran radiative transfer model, solar radiation levels at Earth’s surface are computed for five distinct levels of solar activity to predict erythemal, DNA damage, and vitamin D radiation doses between 2100 and 2199. This process requires weighting the relevant wavelength bands with their respective action spectra. In relation to the reference scenario of continued prevalent solar activity, a decline of 3.5 or 6.5 Wm-2 is found to result in respective relative index increases of 0.72% or 1.18% for erythema, 2.73% or 4.85% for DNA damage, and 1.03% or 1.73% for vitamin D production. Regional differences are also shown to be significant. The greatest relative changes are expected in the midlatitudes: up to 2.12% for erythema, 6.90% for DNA damage, and 3.44% for vitamin D production. Additionally, the northern hemisphere is found to be more affected than the southern hemisphere, displaying 0.45% higher intensity for erythema, 0.98% for DNA damage, and 0.44% for vitamin D production. These findings corroborate expectations derived from future ozone-column simulations. The results also carry important implications for future health protection efforts should a grand solar minimum occur. Education-based measures could prove effective if adapted adequately. However, individual factors play a major role in UV-induced health effects, and thus predictions about overall future impacts on public health remain challenging. Nonetheless, the evidence underscores that efforts to implement effective health protection measures need to be enhanced in a potential GSMi-future given the straightforward and practical prevention strategies available. This is especially true for the northern midlatitudes, where the general population is most at risk and greatest changes would occur.