July 15, 2008

Hail No – It Isn’t Happening!

Who could ever forget one of the opening scenes in The Day After Tomorrow when hailstones the size of basketballs were crashing into Tokyo causing death and destruction. Obviously, the greenhouse alarmists cannot wait to claim that severe storms will increase in frequency and intensity in the future, and nothing drives home the point like a city being punished by killer hail stones.

Amazingly, a search of “Global Warming and Hail” produces over one million hits, although some include the word “hail” as a word to “summon” or “call” for some action and have nothing to do with ice falling from the sky. Nonetheless, there is no end of material with titles about Nebraska towns using snowplows in summer to clear hail, crops being damaged by unusual hail events, and on and on. One of our favorites is “Latest Global Warming Worry: Megacryometeors” – use the word “megacryometeors” at the next greenie cocktail party and you will definitely win the award for outstanding global warming vocabulary!

If one was really interested in hail and global warming, the search might begin with the United Nations Intergovernmental Panel on Climate Change 2007 Summary for Policymakers in which the word “hail” appears only once and in the sentence “There is insufficient evidence to determine whether trends exist in the meridional overturning circulation of the global ocean or in small-scale phenomena such as tornadoes, hail, lightning and dust-storms.” In the 2007 IPCC Technical Summary, the word “hail” is in only one sentence stating “There is insufficient evidence to determine whether trends exist in such events as tornadoes, hail, lightning and dust storms which occur at small spatial scales.” IPCC has yet to use the word “megacryometeor,” but there is still time to work it into the next round of assessments.

Our sudden interest in hail coincides with an article just published in Geophysical Research Letters entitled “Trends in hail in China during 1960–2005” and written by scientists at China’s School of Physics and the Department of Meteorology at the University of Hawai’i. The authors note that the research was funded by Chinese National Science Foundation and “Japan through its sponsorship to the International Pacific Research Center” at the University of Hawai’i. Who knows, maybe that The Day After Tomorrow scene scared the Japanese into funding some research on hail?

Xie et al. begin their article noting that “Studies on hail climatology, especially the long-term variation of Annual Hail Days (AHD, defined as the sum of hail days of all individual stations per year in China), are very important for understanding the regional climate change.” Fair enough, but the trio makes no attempt to forecast any increase in hail in China due to global warming. In describing their dataset, they state “The National Meteorological Information Center (NMIC) of China has compiled a complete historical hail dataset of 753 stations, which includes hail data for all weather stations in the surface meteorological observational network over the whole of China from 1951 to 2005. Because of some unexpected and historical reasons, for instance, some stations were relocated and some were established during this period, not all stations have the complete records of hail.” After some details on their procedures, they conclude “To ensure a relatively large and continuous data records, we chose 523 stations with complete observations from 1960 to 2005 in this study.”

Xie et al. report “We first calculated the trend of the AHD at each station from 1960 to 2005. The trend at each station was then classified into one of the three groups: up trend and down trend (both significant at 95% confidence level), and no trend. Only one station in northwest of China shows up trend of AHD. About 25% stations (131 stations) show distinct down trend of AHD. They are mainly in northwest and northeast of China. The remaining 391 stations (accounting for about 74% of all stations) show no significant trend from 1960 to 2005. Most of these stations are located in south of China.” The two plots below reveal the strength of the downward trend in hail events in China over the past 25 years.

Figure 1. Mean AHD variations and trends, respectively, in the whole of China, south of China, and north of China during 1960–2005 (from Xie et al., 2008)

Figure 2. (left) The mean hail frequency against month and year (filled color) and (right) mean seasonal variation (blue bar) of hail frequency and their trends (red curve, and each green square indicates that the down trend is significant at 95% confidence level) in China from 1960 to 2005. Note that the dashed lines (right) show the 95% confidence intervals (from Xie et al., 2008).

Xie et al. conclude “Hail records provided by NMIC from 1960 to 2005 were used to analyze the long-term trend in annual hail days in China. Two distinct periods in the 46 years were identified. In the first period (1960-early 1980s), AHD showed little linear trend, while in the second period (early 1980s and afterwards), there was a significant down AHD trend days. This down trend in AHD was mainly contributed by the down trend in warm season during June–September. Analysis of some climatic factors indicated that the rising trend in freezing-level height, which increased by about 200 m during 1960–2005 is responsible for the decreasing trend in hail frequency.”

Their final sentence is our favorite as the clearly state “The results from this study may imply a possible reduction of hail occurrence under the global warming due to the increase in freezing-level height in China.”


Xie, B., Q. Zhang, and Y. Wang (2008), Trends in hail in China during 1960–2005, Geophysical Research Letters, 35, L13801, doi:10.1029/2008GL034067.

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