Christine, Article.. 20th CENTURY TEMPERATURES ATOP MT. WASHINGTON..
Long-term continuous temperature records from remote areas away from the contaminating effects of rapid human population growth and associated land-use changes are of special interest in the greenhouse debate. One such long-term record from the northeastern United States comes from an observatory that has been operating continuously since 1932 at the summit of Mount Washington, New Hampshire. Given the quality and completeness of these records, the lack of any urban influence at the site, the analysis of climate variations at Mount Washington is useful in examining temperature trends (or lack thereof) during the period of historical records.
Mount Washington is located in the Presidential Range, New Hampshire, at 44°16'N, 71°18'W, with a summit elevation of 6,288 feet. While surrounding mountain ranges peak at about 4,000 feet, Mount Washington's elevation exposes its summit above the surrounding mountainous plateau. Its high elevation, unique exposure, and location along major storm tracks subjects Mount Washington to low temperatures, high winds, fog, rain, and snow throughout the year.
The Mount Washington Observatory, located on the summit, was founded in 1932 as a private, non-profit corporation to conduct scientific research and meteorological observations. The Observatory is the only fully-staffed, year-round alpine weather observatory in continental North America. Observations are taken by the staff members every three hours and the data are reported in near real-time to the National Weather Service. Reports consist of wind speed and direction, wet-bulb and dry-bulb temperatures, barometric pressure, relative humidity, precipitation, snowfall, and cloud cover.
All instruments and instrument locations used in this century at Mount Washington are approved, certified, and meet the specifications of the National Weather Service. All weather observations have been made within 200 feet of the geological summit of Mount Washington. Land-use changes in the immediate vicinity of the meteorological equipment have been minimal throughout the length of data collection. We obtained the minimum and maximum temperature data for the period 1939 to 1997 from the National Climatic Data Center and for 1998 data, we contacted the Observatory directly.
The weather atop Mount Washington may not seem normal to daily visitors, but climatological "normals" for the stations are certainly available (Hildebrandt and Balling, 1998). For example, in balmy July, the normal high temperature is 53.6°F while the low is 43.0°F. Before you get feeling too comfortable, be aware that the normal wind speed is 25.3 mph keeping the mid-summer daytime wind-chill factor well below freezing. And after such a pleasant summer experience, know that the normal high temperature in January is only 12.3°F with lows averaging –4.6°F. Add the normal wind speed of 46.2 mph, and you will find frostbite conditions occurring commonly at the summit. Over 250 inches of snow will fall in an average year, with all twelve months normally experiencing snowfall. And given the fog which persists greater than 70 percent of the time, cold temperatures, and high wind, much of the snow blows away and rime ice grows into the wind often two feet in length covering much of the summit and its buildings. In other words, if you are planning on staying atop Mount Washington, you may want to pack a few warm clothes!
If the normal climate does not seem harsh enough, the records are legitimate killers. The coldest temperature recorded on the summit is –47°F in January 1934; -46°F has been recorded many times at the Observatory. The highest wind speed is the infamous 231 mph on April 12, 1934, and every month through the entire record has seen hurricane-strength winds. The extreme low chill for all months is below –100°F. On the warm side, the highest temperature ever recorded at the station is 72°F reached many times, but never broken.
A plot of the 1939 to 1998 annualized mean, maximum, and minimum temperatures from Mount Washington is shown in Figure 1. The linear increase in mean temperature over the 60-year period is +0.28°F, +0.49°F for the minimum temperatures, and +0.07°F for the maximum temperatures. None of these changes are anywhere close to being judged statistically significant – in other words, we cannot say with confidence that there has been any change in the mean, maximum, or minimum temperature at this site since the Observatory began their operation in the 1930s.
Much of the world has seen a reduction in the diurnal temperature range, and this signal may be a response to the buildup of greenhouse gases (Easterling et al., 1997). The Mount Washington diurnal temperature range fell by 0.42°F over the 60-year period, but the change was not statistically significant. The famous Pic du Midi station located high in the Pyrenees (9,387 feet) does show a significant reduction in the diurnal temperature range over the past century (Bücher and Dessens, 1991; Dessens and Bücher, 1995), but high elevation stations in Switzerland, Germany, and Austria have shown no such significant reduction (Weber et al., 1994). The results from Mount Washington do little to settle any debate on this issue.
Obviously, Mount Washington is just one location on earth, and no one argues that it is some bellwether of global climate. But it is curious that this pristine location seems to show little-to-no response to the buildup of atmospheric carbon dioxide (CO2) and other greenhouse gases through the 20th century. And there appears to be no obvious compensating cooling effects that may have overwhelmed the warming effects of the increased concentrations of CO2. Ozone depletion, with its cooling effects (Hansen et al., 1998), would not impact a station closer to the equator than pole, atmospheric sulfate levels in the region have likely declined in recent decades (Hameed and Dignon, 1988; Husain et al., 1998), and solar radiation levels have increased over this period of data collection at the Observatory (Lean et al., 1995). The general lack of warming may be related to changes in atmospheric circulation or, possibly, some unknown microclimatic effect is masking the expected temperature increase. Or, just possibly, we are all expecting a bit too much from the much-ballyhooed increase in CO2.
Firure 1. Annual maximum, mean, and minimum temperatures (°F) at Mount Washington, 1989-1998.
References
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