Among the highly publicized changes in weather phenomena that are predicted to attend the ongoing rise in the air's CO2 content and temperature are increases in the frequency and severity of all types of storms; and, therefore, in an effort to determine if these predictions have any validity, many researchers have examined pertinent historical and proxy weather records. Although most of these studies focus on storms trends for a given location or region, there have been a few of them that have attempted to examine the issue for the globe as a whole; and in this review we examine what those studies found.
We begin with the study of Huntington (2006), who writes that there is "a theoretical expectation that climate warming will result in increases in evaporation and precipitation, leading to the hypothesis that one of the major consequences will be an intensification (or acceleration) of the water cycle (DelGenio et al., 1991; Loaciga et al., 1996; Trenberth, 1999; Held and Soden, 2000; Arnell et al., 2001)." In addition, he reiterates the long-held climate-model-derived notion that "an intensification of the water cycle may lead to changes in water-resource availability," i.e., "floods and droughts," as well as "an increase in the frequency and intensity of tropical storms." And he thus proceeds to explore these several theoretical expectations via a review of the current state of science regarding historical trends in hydrologic variables, including precipitation, runoff, soil moisture and a number of other parameters. So what did he find?
"On a globally averaged basis," according to Huntington, "precipitation over land increased by about 2% over the period 1900-1998 (Dai et al., 1997; Hulme et al., 1998)." He also notes that "an analysis of trends in world continental runoff from major rivers from 1910-1975 found an increase in runoff of about 3% (Probst and Tardy, 1987)," and that a recent re-analysis of these trends for the period 1920-1995 "confirmed an increase in world continental runoff during the 20th century (Labat et al., 2004)."
All of these findings suggest that global warming may indeed have intensified the global hydrologic cycle over the course of the 20th century. However, Huntington also reports that "the empirical evidence to date does not [italics added] consistently support an increase in the frequency or intensity of tropical storms and floods." As for droughts, he says the "evidence indicates that summer soil moisture content has increased [italics added] during the last several decades at almost all sites [italics added] having long-term records in the Global Soil Moisture Data Bank (Robock et al., 2000)."
In light of such findings, there appears to have been a slight intensification of the hydrologic cycle throughout the 20th century over the totality of Earth's land area, which may or may not have been caused by the concomitant warming of the globe; but it also appears there was no intensification of deleterious weather phenomena such as tropical storms, floods and droughts. In addition, the study of Smith et al. (2006) demonstrates that over the period 1979 to 2004, when climate alarmists claim the planet experienced a warming that was unprecedented over the past two millennia, there was no net change in global precipitation (over both land and water). Consequently, several of the most basic "theoretical expectations" of the climate modeling enterprise appear to have little real-world support in 20th-century hydrologic data.
Exploring global storm trends from another perspective was Gulev and Grigorieva (2004), who analyzed ocean wave heights (a proxy for storms) using the Voluntary Observing Ship wave data of Worley et al. (2005) to characterize significant wave height (HS) over various ocean basins throughout all or parts of the 20th century. In doing so, the two Russian scientists report that "the annual mean HS visual time series in the northeastern Atlantic and northeastern Pacific show a pronounced increase of wave height starting from 1950," which finding sounds pretty much like it vindicates model projections of increasing storms. "However," as they continue, "for the period 1885-2002 there is no secular trend in HS in the Atlantic," and "the upward trend in the Pacific for this period ... becomes considerably weaker than for the period 1950-2002."
Gulev and Grigorieva also note that the highest annual HS in the Pacific during the first half of the century "is comparable with that for recent decades," and that "in the Atlantic it is even higher than during the last 5 decades." In fact, in the Atlantic the mean HS of the entire decade of the 1920s is higher than that of any recent decade; and the mean HS of the last half of the 1940s is also higher than that of the last five years of the record. In the Pacific it also looks like the mean HS from the late 1930s to the late 1940s may have been higher than that of the last decade of the record, although there is a data gap right in the middle of this period that precludes a definitive answer on this latter point. Nevertheless, it is clear that annual mean wave height (a proxy for storminess) over the last decade of the 20th century - when climate alarmists claim global temperatures were warmer than at any other time in the past two millennia - was not higher than annual wave height values that occurred earlier in the century.
Last of all, Key and Chan (1999) analyzed trends in seasonal and annual frequencies of low-pressure centers (cyclones) at 1000-mb (near-surface) and 500-mb heights for six latitude regions (0-30°N, 0-30°S, 30-60°N, 30-60°S, 60-90°N and 60-90°S) over the four-decade period 1958-1997, while also determining trends in cyclone frequencies for El Niņo vs. La Niņa years.
In considering Key and Chan's results for all latitudes, trends in cyclone frequency at both atmospheric levels turned out to be pretty much of a wash, with both positive and negative trends (some significant and some not) observed over the 40-year period. Cyclone frequencies at both atmospheric levels were also found to be lower at all latitude regions except two (30-60°S and 60-90°S) during El Niņo years, as opposed to La Niņa years. Thus, although Key and Chan found some regional differences in cyclone frequencies, there was no indication of any global trend, positive or negative. Additionally, because the authors' found that fewer cyclones occur during warmer El Niņo years, as opposed to cooler La Niņa years, model-based claims that global warming will result in more global storms appear to be further invalidated.
In closing, we note that although the number of reviews examined in this summary is small, each one presents an independent analysis that runs counter to the climate-model-based claim that storm frequency and intensity will increase as a result of global warming.
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Dai, A., Fung, I.Y. and DelGenio, A.D. 1997. Surface observed global land precipitation variations during 1900-1998. Journal of Climate 10: 2943-2962.
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Hulme, M., Osborn, T.J. and Johns, T.C. 1998. Precipitation sensitivity to global warming: comparisons of observations with HadCM2 simulations. Geophysical Research Letters 25: 3379-3382.
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Smith, T.M., Yin, X. and Gruber, A. 2006. Variations in annual global precipitation (1979-2004), based on the Global Precipitation Climatology Project 2.5° analysis. Geophysical Research Letters 33: 10.1029/2005GL025393.
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Worley, S.J., Woodruff, S.D., Reynolds, R.W., Lubker, S.J. and Lott, N. 2005. ICOADS release 2.1 data and products. International Journal of Climatology 25: 823-842.Last updated 19 December 2012