Implications of climate change on energy demand and growing-degree days

The average temperature in the United States has increased by almost 2ºF since the beginning of the 20th century. Such changes in temperature are expected to continue as the Earth’s climate changes as a result of the effects of human related activities. In addition, severe weather events such as drought and heat waves are expected to increase, and could cause increased stress on various societal sectors like energy infrastructure and agriculture. In response to the changes in climate, heating and cooling demand has changed, along with the length and productivity of the growing season. Metrics for energy demand and for agriculture and ecosystems are expected to continue to respond to the changing climate throughout the 21st century. The metrics most commonly used for energy demand are heating-degree days and cooling-degree days (HDD/CDD hereafter). Since the WWII era, these simple indicators have proven useful to energy utilities and military installations to anticipate heating and cooling demand. Further, a metric used to estimate growing potential for various crops and effects on ecosystems is growing-degree days (GDD hereafter). Along with HDD/CDD, GDD have been used for a long time, and can provide useful insights for issues related to agriculture and ecosystems. Here we present results analyzing historical and future CMIP5 model data, along with various projections into the 21st century. Projections for near-century (2010-2029), mid-century (2040-2059), and end-century (2080-2099) are computed for the contiguous U.S. The regions we consider in the U.S. are those used in the U.S. National Climate Assessment, namely the Northwest, Southwest, North Great Plains, South Great Plains, Midwest, Southeast, and Northeast. In addition, we analyze changing seasonal distributions for HDD/CDD. While classically HDD mainly occur in winter and CDD in summer, these distributions are expected to change shape in a warmer climate. Moreover, the growing season for various crops is expected to increase, and as a result, GDD are calculated on an annual basis. Understanding these new distributions can aid energy utilities in a broad way what to expect in the coming years. While heating demand is projected to decrease by 15-20%, cooling demand is expected to change at a much faster rate (in some areas by 100%). These significant changes in HDD/CDD could prove useful to energy utilities, engineers, and city planners in a changing climate. Also, while increases in GDD could prove beneficial for various crops, this increase by itself is potentially misleading once all future impacts from the changing climate are accounted for