Evolution Of Hurricanes

In the recent years there has been a focus on hurricanes because they have gradually gotten stronger in the past years. Scientists became more alarmed during the latest hurricane seasons because they believe they have seen the effects of the global temperatures on hurricanes. In recent years hurricanes ravaged the earth breaking records all around the world. Japan broke its previous record of 6 typhoons with 10 in 2004(Trenberth 2005). Before the 2005 hurricane season there had never been record of a hurricane in the South Atlantic Ocean, but on that year Brazil encountered its first hurricane. Also in 2005, the US saw its largest number of named storms, 27, the largest number of hurricanes, 14, and it has been the only year with three category
5 hurricanes (Anthes 2006). Because of these over the top records, numerous researchers have studied hurricanes more closely and many believe that as the temperature of the Earth increases the temperature of the oceans will raise producing more hurricanes that are more powerful and destructive. The number or of hurricanes and their intensity is very important to society because they are the costliest natural disasters in the United States and also because the population along the coast has increased (Emanuel 2005). Many of the articles that were published before 2005 are more skeptical about making conclusions about whether hurricanes are linked to global warming or not. These articles focus on the 2004 hurricane season which cost the US more than $40 billion according to the National Hurricane Center (Pielke 2005). Those articles that were published after 2005 agree that there is a linkage between rising sea surface temperatures and hurricanes but they do not know what the linkage is yet. Several of the journals include the major ocean basins where hurricanes are formed which are: North Atlantic Ocean, West Pacific Ocean, East Pacific Ocean, Southwest Pacific Ocean, North Indian Ocean, and the South Indian Ocean (Webster et al. 2005). On the other hand, several other journals decide to focus more on the specific regions of, for example, Emanuel’s studies of 2005 & 2007. In all the studies they mention sea surface temperatures and how they are have been on the rise for the past several years. In Figure 1 from Webster et al. graphs the summer sea surface temperatures of the six major oceans basins where hurricanes occur. All of the lines in the graph have been rising since 1995 except for the East Pacific which dipped in 1995 but started to rise again in 2000. This graph agrees with the analysis of hurricane characteristics in the North Atlantic where they have increased in frequency and intensity since 1995 (Webster 2005). In the last few years there has been a debate of whether hurricane intensity correlates with the graphed rise of sea surface temperatures. Many believe so, but others only believe the intensity of the hurricanes will increase not the frequency. Scientists agree that there is no correlation between increasing sea surface temperatures and the number of tropical storms and hurricanes in the global oceans (Webster 2005). On the other hand, considering only the Atlantic Ocean there is a statistically significant increase which started in 1995 (Webster 2005). When this conclusion is placed with figure 2 of Emanuel’s study in 2007 there is relationship. In the same study done by Emanuel published in 2007 he explains the annual hurricane Power Dissipation Index (PDI). He goes on to explain that the storms PDI depend on the storms intensity, duration and frequency. In figure 2 there has been an increase of total power dissipation index number, duration, and intensity of hurricanes since 1995 only in the North Atlantic graph. In graph (a) Emanuel also found that between 1970 and 2004 the frequency increased by 71%, while duration and intensity increase by 62% and 44%, respectively (Emanuel 2007). In the Western North Pacific there is less of a trend because the numbers stay at a constant rate throughout the years until PDI and intensity dips in 2000. In graph (a) there is also a dip in PDI around 1980 followed by a rise of all four factors in the graph. According to Emanuel duration, intensity and annual number of storms are independent and do not correlate with sea surface temperature as is the PDI, suggesting that the latter may be more fundamentally connected with climate variables than traditional metrics (Emanuel 2007). The conclusion that the intensity of the hurricanes is increasing not the actual frequency can be supported in Webster’s study done in 2005.
In his figure 4 he states that the number of category 1 hurricanes stays stagnant throughout the years but has decreased as a percentage total number of hurricane in 35 years (Webster 2005). He goes on to explain that the trend of category 2 and 3 is minimal in both actual numbers and percentage. On the other hand category 4 and 5 hurricanes have almost doubled in number and in proportion (Webster 2005). These changes have occurred in all the ocean basins not just in the North Atlantic like many studies suggest. In table 1 from Webster’s same study he goes on to explain and break down how from 1975 to 1989 there were less category 4 and 5 hurricanes than in 1990 to 2004. For example, in the West Pacific Ocean during 1975 to 1989 there were a total of 85 category 4 and 5 hurricanes; from 1990 to 2004 there was a great increase from 85 to 116. This pattern is evident throughout the table with total numbers and percentages supporting the conclusion that Webster wanted to prove in his paper which is that hurricanes will become more intense as sea surface temperatures increase
globally. In conclusion, there are still some mixed feelings about whether sea surface temperatures have an effect on hurricanes and if they do are they going to affect their frequency or their intensity?
In the study done by Emanuel, Sundararajan, and Williams in 2008 they concluded that the frequency of the hurricanes will diminish but their intensity will increase in some locations. Emanuel’s later studies published in 2007 and 2005 also expresses there is a trend in increasing numbers of storms and their intensity. Webster expresses in his research paper that he agrees there is a 30 year trend towards more frequent and intense hurricanes (Webster 2005). On the other hand, researchers like Anthes and Pielke are more apprehensive about making conclusions about whether there is an actual trend or not. Anthes states in his study that that no one event or single season should be attributed to changes in climate (2006). He goes on to say that it is too early to accept or to deny that hurricanes are linked to global warming. Pielke declares that it is too premature to make conclusions on this topic and gives three reasons in his paper (2005). He believes that there is no connection between green house gasses and the behavior of hurricanes, that there is scientific consensus that there will be changes in hurricane intensity but it will most likely be small, and lastly that the population’s perception of hurricanes are dwarfed by the influence of its own projections of growing wealth and
population (Pielke 2005). From all six studies done all of them do agree in one thing and that there needs to be more research on this topic in order to make a more solid conclusion and to ensure that there is a correlation between rising sea surface temperatures and hurricanes.