What is true of decreased concentrations of stratospheric ozone?

• A. It will cause cooler global temperatures
• B. It has no effect on human health
• C. Significant increases in skin cancer have already occurred
• D. It will increase rainfall in arid regions

Answer: (C)

Decreased stratospheric ozone lets more UV-B radiation reach Earth's surface. UV-B is energetic enough to damage DNA in skin cells, raising the risk of skin cancers (and also contributing to cataracts and immune suppression). Because the ozone layer blocks UV-B, thinning it means more skin damage from sun exposure, and this has led to noticeable increases in skin cancer in many populations over time.

The other ideas don’t fit: more UV-B at the surface doesn’t cause cooler global temperatures overall—surface climate is influenced by many factors, and ozone depletion is tied mainly to higher UV exposure and health risks rather than a stand-alone cooling effect. It isn’t a direct driver of increased rainfall in arid regions, either; rainfall patterns are affected by broader climate systems, not a straightforward result of weaker ozone.