Several possible Ultraviolet-B Effects on Terrestrial Plants have been investigated, including reduction in yield, alteration in species competition, decrease in photosynthetic activity, susceptibility to disease, and changes in plant structure and pigmentation. Studies carried out on loblolly pine indicate retardation of growth and photosynthesis resulting from enhanced levels of ultraviolet-B (UV-B). Similar effects, including yield reduction, were found in certain rice cultivars. In field study experiments, soybean harvests showed decreases under a simulated 25 percent ozone reduction. Existing microclimatic conditions, such as drought and mineral deficiency, can reduce sensitivity to UV-B, however.
Most field studies of Ultraviolet-B Effects on Aquatic Ecosystems have taken place in the Antarctic region, due to the presence of the ozone hole during the polar springtime, and have focused on the effects on phytoplankton, the primary producers at the base of the Antarctic food web. Phytoplankton are sensitive to increased UV-B doses, resulting in decreased mobility and orientation, and changes in photosynthetic and enzymatic reactions. These effects may lead to reduction in primary productivity, which indirectly affects higher trophic levels. Because humans and other consumers are dependent on higher species such as fish and shrimp, populations outside the local ecosystem are potentially at risk. Prokaryotic microorganisms responsible for nitrogen fixation are also susceptible to UV-B, which could result in changes in the biogeochemical cycling of nitrogen, potentially leading to detrimental effects on plant growth. Other possible indirect effects of higher UV-B stress are decreased planktonic production of dimethylsulfide (DMS), an important source of sulfur and cloud condensation nuclei to the atmosphere, and reduced uptake of CO2 by the oceans.
Global climate may also be influenced by Changes in Tropospheric Chemistry. Studies have suggested that the recent slowdown in the rate of increase of methane levels in the atmosphere may be due, in part, to increased UV-B irradiance in the lower atmosphere. Photochemical smog production in urban areas would also increase under enhanced UV-B levels, reducing air quality and leading to possible effects on human health and agriculture.
Chlorofluorocarbons and potential replacement substances also enter into the global climate picture because of their radiative characteristics. Some of these compounds absorb longwave infrared radiation from the Earth's surface that no other substances absorb, thus adding to the greenhouse effect. The Global Warming Potential of Chlorofluorocarbons and Their Replacements has been evaluated relative to carbon dioxide warming potential. This factor is significant when evaluating whether alternatives to CFCs are suitable for distribution in widespread applications on a worldwide basis.