Degree days are defined as the number of degrees by which the average daily temperature is higher than 65°F (cooling degree days) or lower than 65°F (heating degree days). Degree days reflect changes in climate and are used as a proxy for the energy demand for heating or cooling buildings.
These time series show the annual total number of cooling degree days (red) and heating degree days (blue) for the contiguous United States. Since 1980, the number of cooling degree days has increased and the number of heating degree days has decreased. These changes impact the demand for energy use and increase net electricity demand nationwide.
Increasing U.S. temperatures Affect the Amount of Energy Used For Heating and Cooling
Degree days reflect changes in climate and are used as an indicator for the energy demand for heating or cooling buildings (generally, fossil fuel demand for heating and electricity demand for cooling).
Since around 1980, the number of heating degree days has decreased and the number of cooling degree days has increased relative to the 20th century average. The recent increase in cooling days is driven by more frequent days above 65°F and more frequent extreme high temperatures.
Why It's Important
This indicator is used in utility planning and can support construction decisions. It provides information on the relationship between climate and energy use that can inform mitigation strategies.
As temperatures continue to rise, combined changes in heating and cooling degree days are projected to change patterns of energy use and increase net electricity demand nationwide.
About Heating and Cooling Degree Days
Heating and cooling degree days are calculated by the National Oceanic and Atmospheric Administration (NOAA). Daily temperature values for each region of the United States are used to calculate departures from the 65°F baseline. These values are population-weighted using United States Census Bureau data, such that, for example, the same temperature produces more degree days in New York City than in rural Nebraska.