44-44 Appendix D Letter to Thomas Karl, pp. 48-50 Appendix F Acronyms, pp. 51-51 Page 10 and control its availability. Extremes of precipitation or changes in other portions of the hydrologic cycle can lead to droughts and floods. These are often accompanied by wildfire and severe soil erosion, endangering natural habitats, communities, and resources.
Coastal regions are especially sensitive to changes in sea level.
Human health depends directly on temperature and humidity, both of which contribute to heat stress and influence the transmission of infectious disease and the abundance of allergens. Ultraviolet radiation is necessary for the production of vitamin D, but it also contributes to skin cancer and influences air pollution levels. For each attribute, it is important to quantify the mean state or condition, variability over time scales from days to centuries, character and extent geographically, and the frequency and persistence of extreme values. These climate variables also are relevant because of their importance to detection of climate change and the attribution of such change to a cause. Table 1 lists the combined minimum set of important climate variables.