Max Schadt
Steve Roof
Earth Resources
21 November 2009
Response to “Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming
Environment”
1. The big picture of this study is the possible influences of global warming on tropical storm characteristics. This study questions if there have been global changes in cyclone frequency and intensity throughout the world’s oceans in the past thirty-five years. Additionally, the researchers try to find correlations between changes in cyclone activity and global warming.
The researchers do not specifically mention why this correlation could be important, although it can be inferred that cyclone trends are important to understand due to their destructive tendencies, and the fact that global warming may be making cyclones more dangerous.
2. This study hypothesizes that sea surface temperatures (SST) directly affect tropical storm and hurricane activity. If a connection between SST and cyclone intensity or frequency can be found, then it would be substantial evidence that global warming (which is raising SST) is modulating hurricane and tropical storms throughout the world.
3. The study was set up in a way that separated the variables of SST and tropical storm activity in order to analyze the connection between the two. The necessary SST for tropical storms to occur is a known factor, but there is not as much knowledge on how the recent increases in SST provide a causal mechanism for increases in hurricane activity.

4. The predominant assumption made by the researchers is that their interpretations of the satellite imaging data accurately reflect the actual cyclone activity. This study also assumes that the results are a reflection of induced sea surface temperature changes, rather than just a long-term oscillation of storm variability.
5. The study documented sea surface temperatures, tropical storm intensity, and the occurrence of tropical storm days per year in the global seas in order to determine the annual frequency of tropical storms. The data was based on satellite identification using the Dvorak scheme from the years 1970-2004, with additional information provided by aircraft reconnaissance in certain basins. The study only compiled data from this time period because pre-satellite data has been known for inaccuracies. Tropical storm wind speeds were also collected as means to categorize storm intensity.
6. Over the 35-year examination period, the duration and frequency of tropical storms fluctuated significantly year by year, although there was no overall considerable difference between 1970 and 2004. The northern section of the Atlantic Ocean was the only basin that differed from these results, showing an elevation of duration and frequency. These increases in tropical storm activity were in conjunction with increases in SST in the same basin, which could indicate that global warming was the cause of both. However, dissimilar storm trends in other ocean basins with the same SST changes disassociate the results in the North Atlantic with a developing global tendency.
Although the duration and frequency of cyclones have not changed in the past 35 years on a global level, results suggest that the intensity of these storms have in fact increased. The frequency of category 4 and 5 hurricanes (56 to 67 m/s, and >67 m/s respectively) has increased

from about 20% of the total number of hurricanes to approximately 35% of hurricanes across all ocean basins. The frequency of category 2 and 3 hurricanes has not varied significantly in this same time period. Therefore, since the total number of storms has not increased or decreased, the elevated number of category 4 and 5 hurricanes also directly correlates with a decrease in the number of category 1 storms by the same proportion. Based on the consistency of maximum wind speeds throughout the 35-year time period, the maximum intensity of the category 4 and 5 storms has not changed. Only the proportional frequency of these powerful storms has increased, in comparison to weaker category storms.
7. The results of this study indicated that the researchers’ hypothesize was half-right; the frequency of cyclones in the world’s oceans has not increased, but the intensity of these storms has. This suggests that increases in SST maybe be directly connected with increases in storm intensity across the globe.
8. It is possible that the trend of storm intensity increases may be due to a natural oscillation. Another study suggests that in 1970 there was simply a proportionally small amount of intense storms, which would explain why we have experienced an increasing trend in storm intensity throughout the last 35 years.
9. Further research specifically in the North Atlantic basin seems appropriate, as it was the only area that showed increases in duration and frequency of storms, and therefore may withhold more information. In order to more conclusively link SST to cyclone activity as a global trend, a longer time span of data is needed. Continued study of this topic is of significant importance, as many people are affected by tropical storms and would be endangered by further increases in hurricane intensity. It is essential to establish whether global warming is responsible

for contributing to elevations of hurricane intensity and frequency. This information would give further evidence that global warming is having serious consequences on the earth, and simultaneously give humans further reason to revaluate our attitude towards the planet and its processes.
Works Cited
Webster, P., Holland, G., Curry, J., & Change, H. (2005). Changes in tropical cyclone number, duration, and intensity in a warming environment. Science , 309 , 1844-1846.