From Dr. Roy Spencer's Global Warming Blog
Dr. Roy Spencer
notes: Because of his extensive investigation into some of the incredible high temperatures reported in Death Valley, I asked Bill Reed to comment on my previous blog post in which I maintained the world record of 134 degrees. F The maximum temperature recorded may be about 10 degrees warmer and should not be considered a world record. Here are Bill's initial thoughts on the subject. Also, based on his comments, I might update the chart in my previous blog post with more realistic temperature lapse rate values from the early 20th century, when there weren't enough sites to determine accurate lapse rates.
Author: William T. Reed
Many thanks to Dr. Spencer for investigating the current (very questionable) world heat record and for bringing attention to my Death Valley climate research. From a climatological and meteorological perspective, there are several ways to suggest that the Greenland pasture's reported maximum temperature of 134 degrees Fahrenheit for July 10, 1913, may be invalid.
Dr. Spencer's method here (comparing the Death Valley maximum to the nearest surrounding observatory, and making adjustments for the observatory elevation) does a devastating blow to the veracity of the doubtful observations. It basically shows that the temperatures in the lower troposphere were insufficient to support temperatures well above 125 degrees Fahrenheit in July 1913. and the Death Valley report seems reasonable), all recent maxima at surrounding stations support the Death Valley maxima.
From July 7 to July 14, 1913, Death Valley reported maximum temperatures of 127, 128, 129, 134, 129, 130, 131 and 127 degrees Fahrenheit for 8 consecutive afternoons, but the maximum temperatures from the nearest surrounding weather stations did not support this. The hottest temperatures in Greenland pastures! During the hottest five days, maximum temperatures at the nearest stations deviated from the average by about +4 to +8, while highs at Greenland Ranch were nearly 15 degrees Fahrenheit above the July average. (see table)
From 1911 to 1960, annual maximum temperatures in Greenland pastures ranged from 120 degrees Fahrenheit to 127 degrees Fahrenheit, with the exception of 134 degrees Fahrenheit in 1913. Maximum temperatures at surrounding sites will be well above reported levels. In addition, the heat wave in many areas was hotter than the heat wave in the first half of July 1913. degrees without exceeding 130 degrees Fahrenheit during this period?
In his “bias” chart, Dr. Spencer noted “a significant warm bias in the temperatures reported by Greenland pastures over the previous 10-15 years.” Furthermore, he mentioned that observers may rely to some extent on thermometers other than official instruments. I do think that from the spring into the summer of 1913 observers sometimes compared “house thermometer” readings with official equipment. Official climate tables. However, I haven't found much evidence of this particular type of deviation from standard observing procedures outside of 1913.
I believe that the generally higher “bias” numbers in the early years are primarily due to recent changes in regional weather stations that have resulted in cooler maximum temperatures in the early years and warmer maximum temperatures in later years. For example, the two stations closest to Greenland Ranch in 1913 were Independence Station and Lone Pine Station in Owens Valley. In 1913, water from the Owens River was diverted to Los Angeles, and the Owens Valley gradually dried up. Summer maximum temperatures increase as Owens Lake evaporates, irrigation becomes impossible, farmland is abandoned, and desert-like conditions develop. (Roy's note: In the early years there were only a few monitoring stations within 100 miles of Death Valley, so the temperature lapse rates I calculated from these few stations appear to be biased. I will correct this in a future blog post point and will provide a better estimate of what the average daily maximum Death Valley temperature in July should be.
Additionally, during the early decades of the 20th century, thermometer sheds were (almost always) located above the grass. This results in a very conservative (i.e. cool) maximum at the desert station. Low humidity promotes cooling due to evapotranspiration. In the early decades of the 20th century, desert weather stations were often located in towns and cities surrounded by shade trees and lawns. The resulting maximum temperature reports are very conservative. By mid-century and beyond, urban weather stations are more likely to be located at airports or municipal utility sites, fire stations, or equipment yards. These areas are usually devoid of grass and shade trees. Today, desert weather stations in towns are (almost always!) located on bare ground.
You can imagine the maximum difference between a desert station above regularly irrigated grass and a desert station on bare ground. (Roy's Note: In my experience, unless the vegetation area is fairly large and there is little to no wind, the daily maximum temperature at a weather station is still very dependent on air movement from the larger desert surroundings. But be warned…this is not the same as a poorly placed thermometer next to a brick wall or heat pump, where hot air from an isolated source can increase the daily maximum temperature recorded).
Greenland Ranch Station was originally located above alfalfa grass and adjacent to forty acres of arable and irrigated land.
I believe the new observer in 1913 (Oscar Denton) was rather disappointed with the conservative maximum of the official observing station being located over meadows and close to evaporatively cooled farmland. I think he felt the need to adjust the maximum temperature upwards in 1913.
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