SunapeeNews.com

Welcome to the first of a series of articles from the New London (NH) Energy Committee. This article is by NLEC member Bob Crane. Feed-back is welcome and invited. Please share your comments below or email Alice Sprickman. Members of the NL Energy Committee are: Chet Reynolds (chair) Mark Vernon (vice-chair), Frank Anzalone, John Clough, Bob Crane, Jack Harrod, Hardy Hasenfuss Steve Jesseman. Mike Meller, Fred Peterson and Alice Sprickman.

Climate Change in New London and Vicinity

Global warming has been in the news for years.  Does it affect New London?  How do we know? Mark Twain and others before him remarked that if you do not like the weather in New England, wait a minute and it will change.  In mid-January of this year we had a cold snap.  At our home in New London, the minimum recorded temperature was ten degrees below zero (-10 ˚F).  In Concord, the closest National Weather Service primary local climatological station, the minimum temperature was -24 ˚F.  Does a rare local event such as a cold snap or a heat wave tell us anything about global warming?

Climate data for Concord, NH, has been recorded for more than a century but only the last 61 years of data are readily available from the Internet. The minimum recorded temperature for the years from 1948 through 2008 for Concord was -33 ˚F.   That cold snap was in January, 1984.  Climate data for other locations in New Hampshire are available from the State Climatologist’s web site. The additional data are from regional airports and other cooperative observers.  For the day of the cold snap, the minimum recorded temperature at the airport in Lebanon was -24 ˚F, in Hanover it was -23 ˚F and at the base of Mt. Sunapee it was -18 ˚F.  These observations show cold temperatures at each location for the same day but the temperature differences were 10 or more degrees.

Weather conditions vary from location-to-location within a region such as from Hanover to Concord. A weather statistic such as the coldest minimum daily temperature recorded at each observation site within the region over their complete period of record may be closer to each other than for the locations considered above but for the same day.  For 58 years of observation in Hanover, the minimum observed temperature was -30 ˚F; for 41 years in Lebanon, the minimum was -34 ˚F; for 48 years at Mt. Sunapee, the minimum was -26 ˚F; for 17 years in Newport, the minimum was -40 ˚F; and for 8 years in New London, the minimum was -20 ˚F.  For record durations of more than 30 years, the minimum temperatures differ from the average of the minimum temperatures by less than 5 degrees.

The National Weather Service uses averages over a 30-year period to estimate the local climate values called “normals”.  New normals are generated every decade.  The current weather normals are for the years 1971 through 2000.  In recognizing that the climate changes slowly, a 30-year interval provides a balance between the variability of shorter period averages of large day-to-day, month-to-month, and location-to-location variations and the stability needed to track small changes in the averaged values that describe the climate.

Seasonal variations in temperature are to be expected.  Weather observers often report daily maxima or minima when a new extreme value occurs for that day.  The year-to-year variations in temperature extremes for a single day-of-the-year can be quite large.  For the day of the year the 1984 cold snap occurred, the 30-year minimum temperature standard deviation was 15 ˚F.  The expected uncertainty of a normal value for that winter day would be in excess 9 ˚F.

Model predictions for the amount of global warming expected over the next century range from 3 to 7 ˚F depending on the estimated increase in greenhouse gasses.  Significant additional averaging of the observations at a single location is required to reduce the statistical uncertainty of a normal value to one useful in assessing any warming.  The usual approach is to average the observed daily minimum and maximum values over a meteorological season and the 30-year interval used to create the normal value.

The weather service computes the average daily temperature by averaging the maximum and minimum value for that day.   The data for Concord contains two independent 30-year intervals, 1948 through 1977 and 1978 through 2008.  The average temperatures for the 30-year winter month intervals (December, January and February) were 22.5 ± 1.4 ˚F for the first interval and 23.8 ± 1.2 ˚F for the second interval. The average temperatures for the 30-year summer month intervals (June, July and August) were 66.8 ± 0.7 ˚F for the first interval and 67.6 ± 0.6 ˚F for the second interval.  These results show a small increase in average temperature from the first to second interval, which is consistent with current global warming predictions.

By Robert K. Crane, Ph.D.
Professor Emeritus of Meteorology and
Professor Emeritus of Electrical Engineering
University of Oklahoma