Degree Days Shuffle

UC Berkeley campus on a summer day.

A 2015 study, “Impacts of global warming on residential heating and cooling degree-days in the United States,” comparing heating degree-days (HDD), cooling degree-days (CDD), and HDD + CDD across the United States during the historical period 1981–2010 and the future period 2080–2099 predicts that New York City weather will become more like today’s Oklahoma City weather and Seattle’s will become more like present day San Jose’s weather. In general, there will be a significant decrease in HDD days in the North and a significant increase in CDD in the North and South.

The authors, Yana Petri and Ken Caldeira, use a “business as usual” climate model to predict changes in both HDD and CDD in regions across the United States and in particular, for 25 U.S. cities. Among their findings: San Francisco will be the city with the lowest number of HDD + CDD—a measure of heating and cooling energy use—with 2,634 combined degree-days. Minneapolis will be one of the highest in terms of combined HDD and CDD, with 7,174. Interestingly, for San Francisco, that represents a few hundred degree-days less than today and for Minneapolis, more than a thousand less.

On a national scale, the U.S. Climate Change Science Program looked at about 20 studies of climate change since 1990. They predict a 9.2% energy reduction for heating and a 5–20% increase for cooling per 1 °C of temperature change. In the worst-case scenario, worldwide average temperatures will increase by nearly 5 ⁰C. The result? Some heating dominated areas will become cooling dominated. In general, that means less natural gas and fuel oil used and a lot more electricity used for cooling.