Age and livability in a hotter climate.

Men and women over the age of 65 years comprise the most vulnerable population to increasing heat events associated with climate change. One measure of risk involves the physiological determination of the boundary conditions between compensable (thermal balance possible) and uncompensable (continually rising core temperatures) heat strain. The PSU H.E.A.T. (Human Environmental Age Thresholds) Project conducted 273 human subject-based environmental chamber experiments designed to establish critical environmental limits for a cohort of men and women ranging in age from 65 to 92 yrs, both at rest and at a metabolic rate reflecting activities of daily living (i.e., "livability"). Each critical environmental limit comprises a combination of ambient temperature and relative humidity that reflects the upper extremes of livability for older adults. This review documents and provides an overview of the procedures and seminal findings from the project specific to adults over the age of 65 yrs. Predicted changes in the over-65-year-old population in the United States and the consequent impact of climate change projections on future livability are also presented.