Typical climate conditions for the 20th century may not provide the full range of temperature, precipitation and humidity extremes that likely will be encountered for the built environment of the 21st century. It is important to understand the impact of changing climate on building energy consumption, building design and thermal comfort in existing buildings. Therefore sensitivity studies were conducted for an exemplary location: Mason City Iowa. Based on future scenario climates for the period 2040-2070 produced by eight global/regional climate models, future typical meteorological year (FTMY) data sets were developed for this location and basic energy calculations were conducted in Energy Plus for a typical residence as well as the US DOE commercial reference buildings. Our results show that the increase in energy consumption resulting from projected change in climate over the next 50 year at this location results primarily from responding to an increase in ambient humidity in summer. Therefore, the largest energy cost for maintaining desired levels of health and comfort in the future at this location will be attributed to managing higher ambient humidity levels. Put another way, in order to reduce energy consumption by buildings at this location in the future, priority should be given to finding innovative ways to manage humidity or to adapt.