Neither Katrina or any other hurricane or cyclone can be attributed to anthropogenic global warmingOctober 26, 2007
The high court of London found that An Inconvenient Truth “uses emotive images of Hurricane Katrina and suggests that this has been caused by global warming” which is simply not provable.
The deadliest cyclone in recorded history was Cyclone Bhola, which struck Bangladesh (then part of Pakistan) in 1970. Estimates for the number killed range from 200,000 to 1,000,000 people. Like Katrina, this storm was classified as a category 3 when it made landfall. But unlike Katrina it did not have minute by minute satellite tracking. What was its maximum wind speed while it was over the ocean? It was reported to be 185 mph the day it made landfall, but nobody knows for sure. I’d like to show some large high resolution color pictures of the devastation and the suffering of the people, just like Al Gore did for Katrina, but there are few to be found. You can see several grainy low resolution black and white pictures here.
There were no cell phone cameras, few personal cameras and few, if any, television cameras in Bhola at that time. Although there were at least a hundred times the number of casualties due to the Bhola cyclone than due to Hurricane Katrina, most people today have never heard of the Bhola cyclone. Those in the United States that do remember Cyclone Bhola are probably fans of George Harrison’s “The Concert for Bangladesh.” (A great concert. by the way, featuring Harrison, Ringo Starr, Bob Dylan, Eric Clapton and more.)
If you google “Katrina” and “hurricane” you will get 34 million hits. If you google “Bhola” and “cyclone” you will get 10 thousand hits. 3,400 hits on Katrina for every one hit on Bhola. Shortly after Cyclone Bhola the Bulletin of the American Meteorological Society published a paper by Neil Frank of the National Hurricane Center in Florida and S.A. Husain of the Pakistan Meteorological Department entitled “The Deadliest Tropical Cyclone in History?” They list five other hurricanes where the loss of life is believed to be more than 100,000 people. Four of the five are all prior to the 20th century. But the numbers are highly speculative. Before the days of mass communication its was hard to tell how many people died due to a storm in a neighboring village, let alone on the other side of the Earth.
The same effect holds for judging the meteorological parameters of storms. Since the 1970s tropical cyclones have been tracked from space with continuously improving technology. Aircraft have been used to study and track hurricanes starting in the mid 1940s. Prior to that, tracking relied of data from ships and islands while the storms were at sea, and from land side observations once a storm hit shore. So, as technology has advanced, the quality of data has advanced.
J.P. Kossin of the Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison, wrote in the Journal Geophysical Research Letters (2007) that “The variability of the available data combined with long time-scale changes in the availability and quality of observing systems, reporting policies, and the methods utilized to analyze the data make the best track records inhomogeneous by construction” Even in the short satellite era the quality of the data has continuously improved so that Kossin says “the known lack of homogeneity in both the data and techniques applied in the post-analyses has resulted in skepticism regarding the consistency of the best track intensity estimates.” Kossin, et. al., re-analysed the satellite data used in the frequently cited paper by Webster that purported to show an increasing trend in tropical cyclones in the six major cyclone basins (West Pacific, East Pacific, South Pacific, Northern Indian, Southern Indian and North Atlantic). But first they made the data quality consistent by reducing the spatial and temporal resolution of the newer data to match the resolution of the older data (8 kilometers and 3 hours).
Kossin, et. al., found that the global increasing hurricane trend reported by Webster disappeared when data of consistent quality were used. While Webster found increasing trends in 5 of the six basins, Kossin found a significantly increasing trend in only one basin (the North Atlantic). In fact Kossin found a small decreasing global trend.
Christopher Landsea (of the NOAA National Hurricane Center) et. al., drew similar conclusions in the Journal Science in 2006. He points out that in 1975 there were only two geostationary satellites with 9 km resolution used to monitor tropical storms. Today there are eight geostationary satellites with 4 km resolution to do the same monitoring. More important than the number of satellites is the fact that with only two satellites much of the imagery is from oblique angles. Consequently, “The resulting higher resolution images and more direct overhead views of tropical cyclones result in greater and more accurate intensity estimates in recent years.” Lansea explains that the satellite image pattern recognition method, called the “Dvorak Technique,” which is relied on to make storm intensity estimates is highly subjective and tends to give different results when applied by different analysts. Originally the Dvorak Technique was applied only to visible light images (that is daylight images), but was later (1984) applied to infrared images as well.
As an example, Landsea shows satellite images of five North Indian Ocean cyclones taken between 1978 and 1989. Each of these cyclones were listed as reaching category 3 at the time. But reanalysis of the these images using current procedures would result in the storms being classified as category 4 or category 5 today. The implication is that even during the satellite era storm intensity was underestimated in the past compared to the present.
Is the satellite era long enough to judge whether current level of tropical cyclone activity falls outside the natural range?
The only way to answer this question is through paleoclimatological studies. A variety of such studies relating to this question have been done. The paleoclimatological evidence is quite clear: Current hurricane and cyclone activity is NOT unusual from a long term perspective. Several examples of such studies follow:
1. In Low Atlantic hurricane activity in the 1970s and1980s compared to the past 270 years, Nyberg, et. al., point out that “reliable observations of hurricane activity in the North Atlantic only cover the past few decades.” It is not possible to say, based on this short set of data, if the variation that has been seen during these few decades is greater than should be expected over longer time scales. However, they developed a proxy for both sea surface temperature and vertical wind shear covering 270 years. (Vertical wind shear is inversely related to hurricane formation). The result shows that “the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s, reaching anomalously low values during the 1970s and 1980s.” It seems clear that the upswing in hurricane activity seen from the beginning of the satellite era to the present is largely a consequence of the beginning of the satellite era being at the low point of hurricane activity for the last 270 years.
2. The article in Nature, “Intense hurricane activity over the past 5,000 years controlled by El Nin˜o and the West African monsoon,” by Donnelly and Woodruff of the Woods Hole Oceanographic Institution in Massachusetts echos the concern that “the instrumental record is too short and unreliable to reveal trends in intense tropical cyclone activity.” To overcome these limitations they used sediment deposits in coastal lagoons of the Caribbean to gauge hurricane activity on the century and millennial time scales over a 5000 year period. They found the frequency of intense hurricanes varied widely on these time scales during the past 5,000 years and that the frequency appears to be governed by the El Nin˜o/Southern Oscillation and the strength of the West African monsoon.” Additionally, ” sea surface temperatures as high as at present are not necessary to support intervals of frequent intense hurricanes.”
3. The short instrumental record of hurricane activity was a motivation for Miller, et. al. in their 2006 Proceedings of the National Academy of Sciences paper, “Tree-ring isotope records of tropical cyclone activity.” As trees grow, the oxygen isotope ratios of the water at that place and time are locked into their rings. It is also known that the precipitation of tropical cyclones and hurricanes have oxygen isotope ratios that are greatly different that more common causes of precipitation. Miller, et. al., examined long leaf pines (pinus pulustris) in Georgia because they have shallow roots and a distinct early season growth and late season growth in their rings. these combine to give a precise temporal fix on isotope ratio variation. Their study covered 1770 to 1990. Their analysis of the tree ring oxygen isotope data shows very close agreement with the instrumental data for the southeastern United States after 1940, verifying the efficacy of their method for earlier times. The overall results indicate “systematic, decadal- to multidecadal-scale variations” in the isotope ratios, and consequently variations in the number of hurricanes. Hurricane activity appears to have peaked in the 1770s, 1800s to 1820s, 1840s and 1850s, 1865 to 1880, and the 1940s to 1950s. The quietest decades are the 1780s through 1790s, and the 1970s. The 1970s saw the beginning of satellite tracking of hurricanes. The fact that there has been an upswing in hurricanes in the satellite record is much less alarming when you consider that the 1970s was one of the least active decades (at least for the southeastern United States) in over 200 years.
It is quite clear, based on the best analysis of satellite data and paleoclimatological data, that the high court of London ruled correctly when saying that Al Gore had not proved his case when implying that Hurricane Katrina could be attributed to anthropogenic global warming.
Jeffrey P. Donnelly & Jonathan D. Woodruff, “Intense hurricane activity over the past 5,000 years controlled by El Nin˜o and the West African monsoon,” Nature, Vol 447, 24 May 2007 (Get copy here)
Neil L. Frank and S.A. Husain, “The Deadliest Tropical Cyclone in History?,” Bulletin of the American Meteorological Society, Vol 52 No. 6, June 1971 (Get copy here)
J. P. Kossin, “A globally consistent reanalysis of hurricane variability and trends,” Geophysical Research Letters, Vol. 34, 2007 (Get copy here)
Christopher Landsea, et. al., “Can We Detect Trends in Extreme Tropical Cyclones?,” Science, Vol 313, July 2007 (Get copy here)
Dana L. Miller, et. al., “Tree-ring isotope records of tropical cyclone activity,” Proceedings of the National Academy of Sciences, PNAS, Vol. 103, no. 39, September 26, 2006 (Get copy here.)
Johan Nyberg, et. al., “Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years,” Science, Vol 447, 2007. (Get copy here.)
P.J. Webster, et.al., “Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment,” Science 309, 1844 (2005) (Get copy here)