Among the highly publicized doom-and-gloom scenarios that climate alarmists allege to attend the ongoing rise in the air's CO2 content are predicted increases in the frequency and severity of storms. As a result, and in an effort to determine if these predictions have any validity, many scientists are examining historical and proxy storm records in an attempt to determine how temperature changes of the past millennium have impacted this aspect of earth's climate. This summary reviews what some of them have learned about storm trends in North America.
Beginning with eastern North America, 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 in this region. 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."
Similar results were found by Boose et al. (2001). After scouring historical records to reconstruct hurricane damage regimes for an area composed of the six New England states plus adjoining New York City and Long Island for the period 1620-1997, they could discern "no clear century-scale trend in the number of major hurricanes." For the most recent and reliable 200-year portion of the record, however, the cooler 19th century had five of the highest-damage F3 category storms, while the warmer 20th century had only one such storm. Hence, as the earth experienced the warming associated with its recovery from the cold temperatures of the Little Ice Age, it would appear that this part of the planet (New England, USA) experienced, if anything, a decline in the intensity of severe hurricanes.
Going back even further in time, Noren et al. (2002) extracted sediment cores from thirteen small lakes distributed across a 20,000-km2 region of Vermont and eastern New York, finding that "the frequency of storm-related floods in the northeastern United States has varied in regular cycles during the past 13,000 years (13 kyr), with a characteristic period of about 3 kyr." In addition, the most recent upswing in storminess did not begin with what climate alarmists call the unprecedented warming of the 20th century, but "at about 600 yr BP [Before Present], coincident with the beginning of the Little Ice Age." In reality, according to the authors, the increase in storminess was likely a product of natural changes in the Arctic Oscillation.
Moving to southern North America, land-falling hurricanes whose eyes crossed the coast between Cape Sable, Florida and Brownsville, Texas between 1896 and 1995 were the subject of investigation by Bove et al. (1998). With respect to those storms, the authors note that the first half of the 20th Century saw considerably more hurricanes than the last half: 11.8 per decade vs. 9.4 per decade. Ditto for intense hurricanes of category 3 on the Saffir-Simpson storm scale: 4.8 vs. 3.6. In fact, the numbers of all hurricanes and the numbers of intense hurricanes have both been trending downward since 1966, with the decade starting in 1986 exhibiting the fewest intense hurricanes of the entire century.
Liu and Fearn (1993) also studied major storms along the U.S. Gulf Coast, but over a much longer time period: the past 3500 years. Using sediment cores taken from the center of Lake Shelby in Alabama they determined that "major hurricanes of category 4 or 5 intensity directly struck the Alabama coast ... with an average recurrence interval of ~600 years," the last of which super-storms occurred around 700 years ago. They further note that "climate modeling results based on scenarios of greenhouse warming predict a 40% - 50% increase in hurricane intensities in response to warmer tropical oceans," suggestive of the likelihood that if one of these severe storms (which is now about a century overdue) were to hit the Alabama coast again, climate alarmists would be citing its occurrence as vindication of their doomsday predictions. In reality, however, it would be nothing more than an illustration of the age-old adage that history repeats itself.
In another severe storm study, Muller and Stone (2001) examined historical data relating to tropical storm and hurricane strikes along the southeast U.S. coast from South Padre Island, Texas to Cape Hatteras, North Carolina for the 100-year period 1901-2000. The results of their analysis revealed that the temporal variability of tropical storm and hurricane strikes was "great and significant," with most coastal sites experiencing "pronounced clusters of strikes separated by tens of years with very few strikes." With respect to the climate-alarmist claim of a tendency for increased storminess during warmer El Niņo years, the data just didn't cooperate. For tropical storms and hurricanes together, the authors found an average of 1.7 storms per El Niņo season, 2.6 per neutral season, and 3.3 per La Niņa season. For hurricanes only, the average rate of occurrence ranged from 0.5 per El Niņo season to 1.7 per La Niņa season.
In the interior of the United States, Changnon and Changnon (2000) examined hail-day and thunder-day occurrences over the 100-year period 1896-1995 in terms of 20-year averages obtained from records of 66 first-order weather stations distributed across the country. They found that the frequency of thunder-days peaked in the second of the five 20-year intervals, while hail-day frequency peaked in the third or middle interval. Thereafter, both parameters declined to their lowest values of the century in the final 20-year period. Hail-day occurrence, in fact, decreased to only 65% of what it was at mid-century, accompanied by a drop in national hail insurance losses over the same period.
After completing this large regional study, Changnon (2001) turned his attention to an urban and a more rural site in Chicago in an attempt to determine if there might be an urban influence on thunderstorm activity. Over the 40-year period investigated (1959-1998), he found the urban station to have experienced an average of 4.5 (12%) more thunderstorm days per year than the more rural station; and statistical tests revealed this difference to be significant at the 99% level in all four seasons of the year. In view of ongoing population growth over this period, the results of Changnon and Changnon (2000) would thus be considered, if anything, to be conservative, suggesting that the decreases in hail- and thunder-days they found for the interior of the United States over the last half of the 20th century may well have been even greater than what they determined them to be.
Also in the interior of North America, Schwartz and Schmidlin (2002) compiled a blizzard database for the years 1959-2000 for the conterminous United States. A total of 438 blizzards were identified in the 41-year record, yielding an average of 10.7 blizzards per year. Year-to-year variability was significant, with the number of annual blizzards ranging from a low of 1 in the winter of 1980/81 to a high of 27 during the winter of 1996/97. Linear regression analysis revealed a statistically significant increase in the annual number of blizzards during the 41-year period; but the total area affected by blizzards each winter remained relatively constant and showed no trend. If these observations are both correct, then average blizzard size is much smaller now than it was four decades ago. As the authors note, however, "it may also be that the NWS is recording smaller, weaker blizzards in recent years that went unrecorded earlier in the period, as occurred also in the official record of tornadoes in the United States."
The results of this study thus suggest that -- with respect to U.S. blizzards -- frequency may possibly have increased, but if it did, intensity likely did the opposite. On the other hand, the study's authors suggest that the reported increase in blizzard frequency may well be due to an observational bias that developed over the years, for which there is a known analogue in the historical observation of tornados. That this possibility is likely a probability is suggested by the study of Gulev et al. (2001), who analyzed trends in Northern Hemispheric winter cyclones over essentially the same time period (1958-1999) and found a statistically significant decline of 1.2 cyclones per year using NCEP/NCAR reanalysis pressure data.
Further evidence that the blizzard frequency data are observationally-biased can be deduced from the study of Hayden (1999), who investigated storm frequencies over North America between 25° and 55°N latitude and 60° and 125°W longitude from 1885 to 1996. Over this 112-year period, Hayden reports that large regional changes in storm occurrences were observed; but when integrated over the entire geographic area, no net change in storminess was evident.
To the north, Mason and Jordan (2002) studied numerous depositional environments along the tectonically stable, unglaciated eastern Chuckchi Sea coast that stretches across northwest Alaska, deriving a 6000-year record of sea level change, while simultaneously learning some interesting things about the correlation between storminess and climate in that part of the world. With respect to storminess, they learned that "in the Chukchi Sea, storm frequency is correlated with colder rather than warmer climatic conditions." Consequently, they say that their data "do not therefore support predictions of more frequent or intense coastal storms associated with atmospheric warming for this region."
Way north, Hudak and Young (2002) examined the number of fall (June-November) storms in the southern Beaufort Sea region based on criteria of surface wind speed for the relatively short period of 1970-1995. Although there was considerable year-to-year variability in the number of storms, there was no discernible trend over the 26-year period in this region of the globe where climate models predict the effects of CO2-induced global warming to be most evident.
In conclusion, as the earth has warmed over the past hundred and fifty years, during its recovery from the global chill of the Little Ice Age, there has been no significant increase in either the frequency or intensity of stormy weather in North America. In fact, most studies suggest just the opposite has likely occurred. This observation -- coupled with the fact that storminess in many other parts of the planet has also decreased or held steady as the world has warmed -- thus suggests there is no data-based reason to believe that storms anywhere will become either more frequent or more intense if the world warms a bit more in the future.
References
Boose, E.R., Chamberlin, K.E. and Foster, D.R. 2001. Landscape and regional impacts of hurricanes in New England. Ecological Monographs 71: 27-48.
Bove, M.C., Zierden, D.F. and O'Brien, J.J. 1998. Are gulf landfalling hurricanes getting stronger? Bulletin of the American Meteorological Society 79: 1327-1328.
Changnon, S.A. 2001. Assessment of historical thunderstorm data for urban effects: the Chicago case. Climatic Change 49: 161-169.
Changnon, S.A. and Changnon, D. 2000. Long-term fluctuations in hail incidences in the United States. Journal of Climate 13: 658-664.
Gulev, S.K., Zolina, O. and Grigoriev, S. 2001. Extratropical cyclone variability in the Northern Hemisphere winter from the NCEP/NCAR reanalysis data. Climate Dynamics 17: 795-809.
Hayden, B.P. 1999. Climate change and extratropical storminess in the United States: An assessment. Journal of the American Water Resources Association 35: 1387-1397.
Hudak, D.R. and Young, J.M.C. 2002. Storm climatology of the southern Beaufort Sea. Atmosphere-Ocean 40: 145-158.
Liu, K.-b. and Fearn, M.L. 1993. Lake-sediment record of late Holocene hurricane activities from coastal Alabama. Geology 21: 793-796.
Mason, O.W. and Jordan, J.W. 2002. Minimal late Holocene sea level rise in the Chukchi Sea: Arctic insensitivity to global change? Global and Planetary Changes 32: 13-23.
Muller, R.A. and Stone, G.W. 2001. A climatology of tropical storm and hurricane strikes to enhance vulnerability prediction for the southeast U.S. coast. Journal of Coastal Research 17: 949-956.
Noren, A.J., Bierman, P.R., Steig, E.J., Lini, A. and Southon, J. 2002. Millennial-scale storminess variability in the northeastern Unites States during the Holocene epoch. Nature 419: 821-824.
Schwartz, R.M. and Schmidlin, T.W. 2002. Climatology of blizzards in the conterminous United States, 1959-2000. Journal of Climate 15: 1765-1772.
Zhang, K., Douglas, B.C. and Leatherman, S.P. 2000. Twentieth-Century storm activity along the U.S. East Coast. Journal of Climate 13: 1748-1761.