The Impact of Temperature Trends on Short-Term Energy Demand
September 1, 1999
The past few years have witnessed unusually warm weather, as evidenced by both mild winters and hot summers. The most recent winter was the second warmest on record, and the summer of 1998 set new U.S. and worldwide temperature records. Climatologists have concluded that the recent spate of unusually warm weather is part of a warming trend that dates to 1965, and that this trend is likely to continue. The trend has also exhibited distinct seasonal and regional variations: winters have experienced a greater warming trend than other seasons, and the West has been more prone to warming than the rest of the Lower-48 states.
The analysis shows that the 30-year norms--the basis of weather-related energy demand projections--do not reflect the warming trend or its regional and seasonal patterns. Weather premises based on climate change result in lower energy demand projections. The concentration of the warming trend during the winter season results in a reduction of projected space-heating requirements exceeding increases in summer cooling demand that also result from the same trend.
In a paper published in January 1999, Robert Livezey and Thomas Smith (LS) of the National Oceanographic and Atmospheric Administration (NOAA) found evidence of a quantifiable warming trend starting in 1965. Their models were able to isolate other factors, including El Nino and La Nina episodes, in identifying that trend. LS estimated the average national warming trend to be 0.015 degrees Fahrenheit per year. In other words, average annual temperatures in the Lower-48 states have risen more than half a degree since the onset of the warming trend 34 years ago.
LS also identified widely divergent seasonal and regional patterns in the warming trend. Figure 1 depicts the seasonal and regional nature of climate change. The bar graph shows that the upward temperature trend for the peak winter season averages 0.055 degrees Fahrenheit per year, more than three times that for the year as a whole. In contrast, fall temperatures have exhibited a slight cooling trend. The map of the Lower-48 states highlights the regional variation in annual temperature trends. Western and coastal areas have undergone even more pronounced warming than the national average, while some areas of the Deep South have exhibited mild cooling trends. Figure 2 comprises examples of sharp regional divergences during different seasons compared to those observed on an annual basis.
These findings have prompted a review of the traditional approach to projecting weatherrelated energy demand based on 30-year averages. The analysis below attempts to corroborate the LS findings in terms of data used in generating short-term energy demand projections.