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Extreme Weather Events: Are they Influenced by Rising Atmospheric CO2?

3.3. Storms

Several researchers have investigated how storms have responded to the global warming of the past few decades. This section highlights the results of numerous empirical analyses that shed light on the climate-alarmist claim that CO2-induced global warming is leading to more frequent and intensified storm events around the globe. The studies discussed here clearly indicate there is nothing unusual about storms of the modern era. Severe storms of the most recent decades have historic analogs in the distant and not-so-distant past, when the atmosphere's CO2 concentration was much lower than it is presently. As such, the materials presented below do not support the climate-alarmist contention that the ongoing rise in the air's CO2 content is having a measurable impact on extratropical (non-hurricane) storms.

Hayden (1999) investigated storm frequencies in North America between 25° and 55°N latitude and 60° and 125°W longitude from 1885 to 1996. Over this 112-year period, he reported that large regional changes in storm occurrences were observed; but when integrated over the entire geographic area, no net change in storminess was evident.

Zhang et al. (2000) used ten long-term records of storm surges derived from hourly tide gauge measurements to calculate annual values of the number, duration and integrated intensity of storms along the east coast of the United States. Their analysis did not reveal any trends in storm activity during the twentieth century, which they say is suggestive of "a lack of response of storminess to minor global warming along the U.S. Atlantic coast during the last 100 yr."

Writing as background for their study, Changnon and Changnon (2006) state that (1) "global climate models predict that more weather extremes will be a part of a changed climate due to greenhouse gases," that (2) such a climate change "is anticipated to result in alterations of cyclone activity over the Northern Hemisphere (Lawson, 2003)," and that (3) "a change in the frequency, locations, and/or intensity of extratropical cyclones in the mid-latitudes would alter the incidence of snowstorms," citing the work of Trenberth and Owen (1999). Thus, they decided to see if real-world data could shed any light on the veracity of these predictions, conducting "a climatological analysis of the spatial and temporal distributions of ... damaging snowstorms and their economic losses using property-casualty insurance data that consist of highly damaging storm events, classed as catastrophes by the insurance industry, during the 1949-2000 period."

In describing their findings, the father-and-son research team reports that "the incidence of storms peaked in the 1976-1985 period," but that snowstorm incidence "exhibited no up or down trend during 1949-2000," although national monetary losses did have a significant upward time trend indicative of "a growing societal vulnerability to snowstorms." The two researchers thus concluded their paper by stating that "the temporal frequency of damaging snowstorms during 1949-2000 in the United States does not display any increase over time, indicating that either no [CO2-induced] climate change effect on cyclonic activity has begun, or if it has begun, altered conditions have not influenced the incidence of snowstorms."

Changnon (2003) utilized an extensive data set on thunderstorm days covering the period 1896-1995 to assess long-term temporal variations in thunderstorm activity at 110 first-order weather reporting stations scattered across the United States. By dividing the data into five 20-year segments, Changnon found that "the 1936-1955 period was the nation's peak of storm activity during the 100-year period ending in 1995." During this central 20-year period, 40% of the 110 first-order weather stations experienced their greatest level of storm activity, whereas during the final 20-year period from 1976-1995, only 15% of the stations experienced their greatest level of storm activity.

Gulev et al. (2001) utilized sea level pressure from NCEP/NCAR reanalysis data for the period 1958-1999 to develop a winter (January-March) climatology of cyclones (storms) for the Northern Hemisphere, from which they statistically analyzed only those cyclones that reached a sea level pressure of 1,000 mb or lower. Their results indicated that the yearly mean number of winter cyclones for the period was 234, although there was pronounced interannual and spatial variability in the record. Linear trend estimates indicated a statistically significant (95% level) annual decline of 1.2 cyclones per year, suggesting there were 50 fewer cyclones in the Northern Hemisphere winter at the end of the record than there were during the prior 42 years (Figure 7). Additional data analyses suggest that Northern Hemisphere winter cyclones are intensifying at quicker rates and are reaching greater maximum depths (lower sea level pressure) at the end of the record than they were at the beginning of the record. However, the wintertime cyclones are also experiencing shorter life cycles, dissipating more quickly at the end of the record than at the beginning.

Figure 7. Yearly number of Northern Hemisphere cyclones over the period 1958-1999. Adapted from Gulev et al. (2001).

Winter storms in the Northern Hemisphere at the end of the 20th century thus appear to have been maturing faster, but dissipating quicker, than they were four decades earlier. Could this change be the result of global warming? According to the researchers who performed the analyses, the phenomenon is probably connected to large-scale features of atmospheric variability, such as the North Atlantic Oscillation and the North Pacific Oscillation. As for the large decrease reported in the annual number of Northern Hemisphere cyclones over the 42-year period, this observation is in direct opposition to model-based extreme weather predictions, which suggest that the frequency of such events will increase as a result of global warming.

Recognizing that "media reports in recent years have left the public with the distinct impression that global warming has resulted, and continues to result, in changes in the frequencies and intensities of severe weather events," Hage (2003) set out to test this hypothesis in the prairie provinces of Alberta and Saskatchewan in western Canada. This was accomplished by utilizing "previously unexploited written resources such as daily and weekly newspapers and community histories" to establish a data base adequate for determining long-term trends of all destructive windstorms (primarily thunderstorm-based tornadoes and downbursts) for the region over the period 1882 to 2001. And the results of this study revealed that "all intense storms showed no discernible changes in frequency after 1940," while prior to that time they had exhibited minor maxima.

Focusing on the region of northern and northwestern Scotland, Dawson et al. (2002) searched daily meteorological records from Stornoway (Outer Hebrides), Lerwick (Shetland Islands), Wick (Caithness) and Fair Isle (west of the Shetland Islands) for all data pertaining to gale-force winds over the period 1876-1996, which they used to construct a history of storminess for that period for northern and northwestern Scotland. This history indicated that although North Atlantic storminess and associated wave heights had indeed increased over the prior two decades, storminess in the North Atlantic region "was considerably more severe during parts of the nineteenth century than in recent decades." In addition, whereas the modern increase in storminess appeared to be associated with a spate of substantial positive values of the North Atlantic Oscillation (NAO) index, they say "this was not the case during the period of exceptional storminess at the close of the nineteenth century." During that earlier period, the conditions that fostered modern storminess were apparently overpowered by something even more potent, i.e., cold temperatures, which in the view of Dawson et al. led to an expansion of sea ice in the Greenland Sea that expanded and intensified the Greenland anticyclone, which in turn led to the North Atlantic cyclone track being displaced farther south. Additional support for this view is provided by Clarke et al. (2002), who postulated that a southward spread of sea ice and polar water results in an increased thermal gradient between 50°N and 65°N that intensifies storm activity in the North Atlantic and supports dune formation in the Aquitaine region of southwest France.

The results of these two studies suggest that the increased storminess and wave heights observed in the European sector of the North Atlantic Ocean over the past two decades are not the result of global warming. Rather, they are associated with the most recent periodic increase in the NAO index. Furthermore, a longer historical perspective reveals that North Atlantic storminess was even more severe than it is now during the latter part of the nineteenth century, when it was significantly colder than it is now. In fact, the storminess of that much colder period was so great that it was actually decoupled from the NAO index. Hence, the long view of history suggests that the global warming of the past century or so has actually led to an overall decrease in North Atlantic storminess.

In introducing their study of the subject, Allan et al. (2009) write that an analysis of a 47-year storm database by Alexander et al. (2005) "showed an increase in the number of severe storms in the 1990s in the United Kingdom," but that "it was not possible to say with any certainty that this was either indicative of climatic change or unusual unless it was seen in a longer-term context." Thus, in an effort to provide a longer-term context to that study, Allan et al. (2009) extended the database of Alexander et al. back to 1920, almost doubling the length of the record, after which they reanalyzed the expanded dataset for the periods of boreal autumn (October, November, December) and winter (January, February, March). And in doing so, they determined that both databases exhibited peaks in storminess in the 1920s and 1990s, with boreal autumn storms being more numerous in the 1920s and winter storms being more numerous in the 1990s. The total storm numbers for each decade are plotted in Figure 8; and as can be seen there, both the beginning and end decades of the record experienced nearly identical numbers of storms, demonstrating that the increasingly greater number of extreme storms that impacted the British Isles from the 1960s through the 1990s likely was not related to the global warming of that period.

Figure 8. Number of extreme storms impacting the British Isles in each of eight decadal periods. Created from results reported by Allan et al. (2009).

Working in Sweden, Barring and von Storch (2004) introduced the rationale for their study by saying that with the popular perspective of anthropogenic climate change, the occurrence of extreme events such as windstorms may "create the perception that ... the storms lately have become more violent, a trend that may continue into the future." Therefore, with the intent to test this inference, and relying on data rather than perception to address the topic, the two researchers analyzed long time series of pressure readings for Lund (since 1780) and Stockholm (since 1823), analyzing (1) the annual number of pressure observations below 980 hPa, (2) the annual number of absolute pressure tendencies exceeding 16 hPa/12h, and (3) intra-annual 95th and 99th percentiles of the absolute pressure differences between two consecutive observations. And by these means they determined that the storminess time series they developed "are remarkably stationary in their mean, with little variations on time scales of more than one or two decades." In this regard, for example, they note "the 1860s-70s was a period when the storminess indices showed general higher values," as was the 1980s-90s, but that, subsequently, "the indices have returned to close to their long-term mean."

Barring and von Storch thus concluded their paper by stating that their storminess proxies "show no indication of a long-term robust change towards a more vigorous storm climate." In fact, during "the entire historical period," in their words, storminess was "remarkably stable, with no systematic change and little transient variability." Thus, it can be concluded that for much of Sweden, at least, there was no warming-induced increase in windstorms over the entire transitional period between the Little Ice Age and the Modern Warm Period, which suggests there is little reason to conclude that this non-trend would change with any further warming of the globe.

Introducing their work, Bielec-Bakowska and Piotrowicz (2013) write that "at a continental scale it is low pressure areas, especially those traveling from west to east with their associated systems of atmospheric fronts, that generally have a significant influence on European weather," as they are "often accompanied by meteorological phenomena of a violent nature, such as sudden changes of pressure and temperature, strong winds, heavy precipitation including hail, and electrical discharges," with the result that "very often these phenomena cause considerable damage to the environment and the economy and may adversely influence human health and well-being." And they add that "at a time of ongoing debate about climate change and the impact of human activities, questions have been asked whether a further increase in the frequency and intensity of similar events might be expected in the near future."

In an attempt to provide a well-founded data-based answer to this important question, Bielec-Bakowska and Piotrowicz analyzed the frequency of occurrence of air pressure values equal to or lower than the 1st percentile (equivalent to ≥ 995.3 hPa) of all air pressure values recorded at 12:00 UTC in Krakow, Poland, over a period of 110 years (1900/1901-2009/2010), with "special attention" being devoted to the tracks of deep cyclones. This work revealed that the frequency of deep cyclones in Poland, both overall and in each of a number of specific track groups, "failed to change significantly" over the 110-year period of their study (see Figure 9 below). And in the most important of these groups, which was composed of "more than half of all deep cyclones," they found they "developed over the Atlantic and travelled over or near Iceland via the Baltic Sea and/or the Scandinavian Peninsula," and that "towards the end of the study period, it was observed that deep cyclones following these tracks shortened their journeys considerably," due to the fact that "as they moved over the Scandinavian Peninsula or the Baltic Sea, they 'suddenly' weakened and filled up."

Figure 9. Long-term variability of the number of days with deep cyclones (≥ 995.3 hPa) in Krakow, Poland over the period 1900-2010. Adapted from Bielec-Bakowska and Piotrowicz (2013).

In the concluding paragraph of their paper, Bakowska and Piotrowicz thus wrote that their study "failed to clearly confirm any increase in the frequency of particularly deep cyclones," which means, as they noted, that "forecasts envisaging higher frequencies of strong winds accompanying deep cyclones must be treated with caution."

Using an historical hail dataset of 753 stations compiled by the National Meteorological Information Center of China, which "includes hail data for all weather stations in the surface meteorological observational network over the whole of China from 1951 to 2005," Xie et al. (2008) "chose 523 stations with complete observations from 1960 to 2005" to use in their study of "annual variations and trend[s] of hail frequency across mainland China during 1960-2005."

As is clearly evident in Figure 10, Xie et al. note that the results of their study "show no trend in the mean Annual Hail Days (AHD) from 1960 to [the] early 1980s but a significant decreasing trend afterwards," which latter downturn, it should be noted, was concomitant with the warming of the globe that the IPCC claims was unprecedented over the past one to two millennia, leading the three authors to conclude that global warming may actually imply "a possible reduction of hail occurrence."

Figure 10. Mean Annual Hail Day variations and trends in northern China, southern China and the whole of China. Adapted from Xie et al. (2008).

In another important study, Xie and Zhang (2010) set out to learn if there had been any change in another type of storm extremeness (hailstone size), noting that "changes in hail size are also an important aspect of hail climatology." Specifically, they examined the long-term trend of hail size in four regions of China over the period 1980-2005, using maximum hail diameter data obtained from the Meteorological Administrations of Xinjiang Uygur Autonomous Region (XUAR), Inner Mongolia Autonomous Region (IMAR), Guizhou Province and Hebei Province. The results of this study revealed an uptrend in maximum hail diameter in Hebei, a flat trend in XUAR, and a slight downtrend in both Guizhou and IMAR; but they add that "none of the trends is statistically significant." And in light of these several findings, it should be clear that the highly-hyped global warming of the past few decades has led to no increase in the extremeness of Chinese hail storms. In fact, the data suggest there was a slight decline in the frequency of such storms, along with a hint of a possible decrease in maximum hail diameter, which latter non-significant observation doesn't really mean very much, except that it strongly suggests there was at least no increase in maximum hail diameter.

Lastly, exploring global storm trends from another perspective, Gulev and Grigorieva (2004) 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 found 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 they note that "the upward trend in the Pacific for this period ... becomes considerably weaker than for the period 1885-2002."

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 any recent decade; and the mean HS of the last half of the 1940s is also higher than the last five years of the record. In the Pacific it also appears 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 the IPCC claims global temperatures were warmer than at any other time in the past one to two millennia - was not higher than annual wave height values that occurred earlier in the century.

The results of the studies described above indicate there has been little to no significant increase in either the frequency or intensity of stormy weather over the past several decades. In fact, most studies suggest that just the opposite has likely occurred. And similar findings are noted when expanding the scope of analysis to cover longer periods of time, as illustrated in the studies described below.

Starting in Australia, Alexander et al. (2011) introduce their study by stating that "understanding the long-term variability of storm activity would give a much better perspective on how unusual recent climate variations have been," and they note in this regard that "for southeast and eastern Australia some studies have been able to assess measures of storm activity over longer periods back to the 19th century (e.g., Alexander and Power, 2009; Rakich et al., 2008), finding either a decline in the number of storms or reduction in the strength of zonal geostrophic wind flow," although noting that these studies "were limited to the analysis of only one or two locations." Therefore, in an effort designed to significantly expand the database employed in their newest study of the subject, Alexander et al. analyzed storminess across the whole of southeast (SE) Australia using extreme (standardized seasonal 95th and 99th percentiles) geostrophic winds deduced from eight widespread stations possessing sub-daily atmospheric pressure observations dating back to the late 19th century.

Based on this endeavor, the four researchers found "strong evidence for a significant reduction in intense wind events across SE Australia over the past century." More specifically, they say "in nearly all regions and seasons, linear trends estimated for both storm indices over the period analyzed show a decrease," while "in terms of the regional average series," they say that "all seasons show statistically significant declines in both storm indices, with the largest reductions in storminess in autumn and winter." Thus, yet another paper illustrates that as the Earth warmed over the last century or more, the climate-alarmist prediction of CO2-induced increases in global storminess is seen to be widely out of sync with reality.

Introducing their study of the subject, Dezileau et al. (2011) write, with respect to extreme weather events, that the major question of the day is: "are they linked to global warming or are they part of natural climate variability?" And in regard to the significance of this question, they say "it is essential to place such events in a broader context of time, and trace the history of climate changes over several centuries," because "these extreme events are inherently rare and therefore difficult to observe in the period of a human life." Only then can claims of increased extreme weather events resulting from CO2-induced global warming be properly evaluated; and Dezileau et al. proceed to do just that. More specifically, the nine researchers analyzed regional historical archives and sediment cores they extracted from two Gulf of Aigues-Mortes lagoons in the northwestern part of the occidental Mediterranean Sea for bio- and geo-indicators of past storm activities there, specifically assessing "the frequency and intensity of [extreme] events during the last 1,500 years," as well as "links between past climatic conditions and storm activities."

Their analysis shows evidence of four "catastrophic storms of category 3 intensity or more," which occurred at approximately AD 455, 1742, 1848 and 1893. And "taking into account text description of the 1742 storm," they conclude that it was "of category more than 4 in intensity," and that all four of the storms "can be called superstorms." In addition, Dezileau et al. make a point of noting that "the apparent increase in intense storms around 250 years ago lasts to about AD 1900," whereupon "intense meteorological activity seems to return to a quiescent interval after (i.e. during the 20th century AD)." And they add that, "interestingly, the two periods of most frequent superstorm strikes in the Aigues-Mortes Gulf (AD 455 and 1700-1900) coincide with two of the coldest periods in Europe during the late Holocene (Bond cycle 1 and the latter half of the Little Ice Age.)" As a result, the authors state that "extreme storm events are associated with a large cooling of Europe," and they calculate that the risk of such storms occurring during that cold period "was higher than today by a factor of 10," noting "if this regime came back today, the implications would be dramatic."

In another study, Ogrin (2007) presented "an overview of severe storms and a reconstruction of periods with their reiterative occurrence in sub-Mediterranean Slovenia in the warm half of the year during the so-called pre-instrumental period," based on "data gathered in secondary and tertiary historical sources." Speaking of "violent storms" and "the periods in which these phenomena were more frequent and reached, as to the costs of damage caused, the level of natural disasters or even catastrophes," Ogrin reports "the 17th and 18th centuries were undoubtedly such periods, particularly their first halves, when besides storms also some other weather-caused natural disasters occurred quite often, so that the inhabitants, who mainly depended on the self-subsistent agriculture, could not recover for several years after some consecutive severe rigors of the weather." In addition, he reports that "the frequency of violent storms in that time was comparable to the incidence towards the end of the 20th century."

Ogrin further writes that the late 20th-century increase in violent storms "is supposed to be a human-generated consequence of emitting greenhouse gasses and of the resulting global warming of the atmosphere." However, in light of his findings, he reports that "the damage done by severe storms in the past does not differ significantly from the damage in the present." And this fact suggests that the weather extremes of today, which he says are "supposed to be a human-generated consequence of emitting greenhouse gasses and of the resulting global warming of the atmosphere," may well be caused by something else; for if they have occurred in the past for a different reason (and they have), they can be occurring today for a different reason too.

Finally, introducing their study, Barring and Fortuniak (2009) say that "extra-tropical cyclone frequency and intensity are currently under intense scrutiny because of the destruction recent windstorms have brought to Europe," adding that "several studies using reanalysis data covering the second half of the 20th century suggest increasing storm intensity in the northeastern Atlantic and European sector." Against this backdrop, Barring and Fortuniak analyzed the "inter-decadal variability in cyclone activity over northwestern Europe back to AD 1780 by combining information from eight storminess indices applied in a Eulerian framework," which indices "use the series of thrice-daily sea level pressure observations at Lund and Stockholm."

The two Swedish scientists say their results show that former reanalysis studies "cover a time period chiefly coinciding with a marked, but not exceptional in our 225-year perspective, positive variation in the regional cyclone activity that has more recently reversed," noting that "because of the inter-decadal variations, a near-centennial time perspective is needed when analyzing variations in extra-tropical cyclone activity and the associated weather conditions over northwestern Europe." And by taking this more proper approach, the two researchers found that (1) "there is no significant overall long-term trend common to all indices in cyclone activity in the North Atlantic and European region since the Dalton minimum," that (2) "the marked positive trend beginning around 1960 ended in the mid-1990s and has since then reversed," and that (3) "this positive trend was more an effect of a 20th-century minimum in cyclone activity around 1960, rather than extraordinary high values in [the] 1990s."

Viewed together, the studies discussed above, based on empirical observations, suggest there is no data-based reason to accept the climate-alarmist contention that storms will become either more frequent or more intense if the world warms a bit more in the future.

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