The higher frequency and intensity of sustained heat events have
increased demand for cooling energy across the globe. Current estimates
of summer-time energy demand are primarily based on Cooling Degree Days
(CDD), calculated using a predetermined comfort zone temperature.
Through a comprehensive analysis of the observed trends in energy demand
across the USA, we show that the current estimates of cooling demand
fall significantly short (±25%) of capturing regional comfort zones.
Moreover, given the increasingly compelling evidence that air
temperature alone is not sufficient for characterizing human thermal
comfort, we extend the widely-used CDD calculation to heat index, which
accounts for both air temperature and humidity. Our results demonstrate
a significant underestimation of the projected climate-sensitive portion
of cooling demand (≈22%) when humidity is ignored. Our findings have
significant implications for the security, sustainability, and
resilience of the grid under climate change.