Although the first two periods revealed statistically significant trends for one of the series, Period III exhibited statistically significant trends for both heating and cooling were statistically significant, corroborating the presence of a warming trend during that interval. The trend estimates, however, should be treated with caution. Period III comprises high volatility in both data series. Some of the coldest winters occurred during the earlier part of period, contributing to possible overstatement of the downward trend. That timeframe also witnessed the three coolest summers.
Trends are also susceptible to the erratic nature of some of the most recent annual data.
Absent the record high data-point for 1998, the CDD trend for Period III would have been much flatter. In addition, the short-term nature of the timeframes renders these findings vulnerable to future shifts in temperature trends as well as pending revisions to early 1999 HDD data. It results largely from data-points near both ends of the period. Indeed, the LS study does not acknowledge the presence of that cooling trend due to the brevity of that timeframe. In contrast to the findings in the LS study, our model was unable to verify the extent to which impacts of El Nino and La Nina episodes affected HDD or CDD readings because of data complexities and differences in modeling techniques.