Research Paper on Hurricane Intensity in the Recent Past

Introduction

Hurricanes are tropical storms that originate from the Atlantic Ocean, and have wind speeds that exceed 74 mph (Aboff & Sotirovski, 2012). In order for a hurricane to form the ocean temperatures have to be over 26 degrees. Although scientists do not know the exact mechanism that leads to hurricane formation, they state that they form in low pressure systems that contain warm, and moist air. The warm air will then rise, release heat, and moisture into the atmosphere (Aboff & Sotirovski, 2012). As the moisture rises it cools and condenses forming clouds, and bands of thunderstorm. There is also a column of air that acts like a chimney drawing warm moist air upwards. In addition to that the Coriolis force leads to the rotation of the rising air, and clouds, and therefore the creation of strong winds. The energy that is normally released from the condensation of the rising, moist air acts as a fuel to the hurricane (Aboff & Sotirovski, 2012). It also explains why a hurricane is at its strongest while in the ocean, and its force decreases considerably as it moves towards the land (the supply of the warm, moist air normally reduces).

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The hurricane season normally begins on June 1st, and lasts up to November 30th. However, it is important to point out that hurricanes can, and have occurred on other occasions other than in the hurricane season. According to the National Oceanic, and Atmospheric Administration (NOAA), hurricanes occur approximately 12 times a year in the Atlantic basin. However, during the hurricane season of 2004, it was reported that there were 23 hurricanes that the struck the Caribbean, Mexico, and other southern regions of the United States. Analytical studies of hurricane characteristics in the North Atlantic region have shown that there has been an increase in hurricane frequency, and intensity since 1995 (Elsberry & Harr, 2013). There has also been a debate in regards to the relationship between the increasing hurricane frequency, and intensity, and increasing sea surface temperature (SST). In this paper, it seeks to answer the following research questions:

Has human activity (greenhouse gas emissions) resulted in an increase in the Atlantic hurricane activity?

Is the devastating, and damaging a depiction of the increased intensity of the hurricanes, or is it a function of the increased density of populations in the areas that hurricanes are likely to strike?

Effect of Anthropogenic Activities

In order for a hurricane to form, there has to be a tropical disturbance on warm ocean waters, and rain clouds forming. As it was stated before, this tropical disturbance may either lead to a tropical disturbance, or tropical storm depending on the wind speeds. Occasionally, a tropical depression may transform, and become a tropical storm if its wind speed rises to more than 39 mph, and if they rise, and reach a sustained level of 74 mph, it will lead to a hurricane. It is important to point out that as the ocean-water evaporates near the equator it will rise until there are enormous amounts of the heated moist air, which are being twisted in the atmosphere (Elsberry & Harr, 2013). The winds will normally circle in a counterclockwise manner if they have originated on the north of the equator, or clockwise if they are from the south of the equator. Hurricanes that are in the ocean-water temperatures of over 26 degrees Celsius will continue to collect moisture from the ocean surface, leading them to grow in both its size, and force (Emanuel, 2017). As the hurricane travels towards the land, or reaches cooler water, it will lose some of the power that it had initially generated, and its wind speed will slow down until they can longer be determined as hurricane forces (less than 74 miles per hour). The hurricanes that normally take place in the Atlantic region originate from ocean waters that are located near Africa. They then drift west via the Trade winds, before being 'pushed' north as a result of the prevailing winds that are travelling eastward across the North America. The hurricanes that take place over the Eastern Pacific region originate from the Central American, and Mexican coastal waters.

The Saffir-Simpson hurricane scale is used to determine the hurricane intensity. It defines the intensity using numbers from 1 to 5 (Emanuel, 2005). In this case, 1 represents the low intensity, while 5 represents the high intensity hurricanes. The table below shows the wind speeds of hurricanes of different intensities, their surge, and potential damage.

Intensity Wind Speed Surge Potential Damage

1. 152km/h (95mph) 1.2-1.5m (4-5ft) Trees, mobile homes
2. 176km/h (110mph) 1.8-2.4m (6-8ft) Roofs, mobile homes
3. 208km/h (130mph) 2.7-3.6m (9-12ft) Damaging buildings
4. 249km/h (155mph) 3.9-5.4m (13-18ft) Extreme: flooding, and other major damages
5. 250+km/h (156+mph) Over 5.4m (over 19ft) Catastrophic: houses will be blown away

However, it is important to point out that people should not underestimate the potential damage of a hurricane just because its intensity is defined to be 1. The reason for this is that, the wind speeds of hurricanes (regardless of their intensity level) is enough to cause damages. Furthermore, hurricanes can also cause flooding, and depending on the location lead to huge damages.

Hurricane experts such as Dr. Yair have noted that there is a disparity in terms of the number, and intensity of hurricanes that occurred between 1975-1989 periods with those that occurred in 1990-2004. There are hurricane experts who attribute the increased number, and intensity of hurricanes to global warming, while others feel that the increased scope of damage is as a result of increased populations in areas that are likely to be hit by the hurricanes (Emanuel, 2017).

The Relationship between Global Warming, and Increased Number, and Intensity of Hurricanes

The observed records of the hurricane activity in the Atlantic region indicate that there is a correlation between the sea surface temperatures (SST) of the Atlantic Ocean, and the Power Dissipation Index (PDI). PDI measures the hurricane activity whereby it combines the frequency, intensity, and also duration of hurricanes using a single index. These records illustrate that there has been an increase of these variables (SSTs, and PDI) since the 1970s (Emanuel, 2017). Model-based climate change studies have shown that there is a link in terms of the increase in the Atlantic SSTs with the increasing greenhouse gases. However, the relationship between the effects of the increasing greenhouse gases, and hurricane PDI is only based on statistical correlations. The statistical linkages provide evidence that show that the increased human activity (greenhouse gases emissions) over the past two, or three decades have resulted in the increased intensity, and frequency of the Atlantic hurricanes. Based on this statistical relationship, hurricane experts are predicting that if the continued anthropogenic influence on the Atlantic hurricanes persist then it would mean that there would be substantial increases in the hurricane destructive potential by up to 300% in PDI by 2100.

Swanson (2008) points out that the Atlantic hurricane PDI is also correlated with different SST indices other than the Atlantic SST. It has been noted that based on this single observation it changes the overall relationship between the greenhouse gases, and the Atlantic ocean PDI (GFDL, 2018). On one hand, the statistical relationship between the Atlantic hurricanes, and the SST is an indication that the hurricane PDI will increase in the 21st century due to greenhouse global warming. On the other hand, the alternative statistical relationship that was proposed by Swanson (2008) implies that greenhouse warming will only have a modest effect on the hurricane PDI. This means that global warming does not have a considerable effect on the hurricane activity (intensity, and also frequency) (GFDL, 2018).

Figure 1: Illustrating the Statistical Relationships between SSTs, and Hurricane PDI

(GFDL, 2018)

The first graph (1a) indicates that there is an absolute correlation between the SST of the Atlantic Ocean, and the PDI, and it is based on the model-based climate change studies that show the link between the increases in the Atlantic SSTs with the increasing greenhouse gases. The second graph (1b) is the one that was proposed by Swanson (2008), and it points out that the Atlantic hurricane PDI is correlated with different SST indices other than the Atlantic SST. As has been indicated in graph (1a) the model-based studies show that because of the increased anthropogenic activities it will have a considerable effect of the hurricane intensity, and frequency, and the change in the PDI will be approximately 300% by 2100 (GFDL, 2018). Graph (1b) shows that even with the continued anthropogenic activities, there will be little changes in the hurricane PDI. This points out that global warming as a single factor cannot lead to considerable changes in the hurricane PDI. The model-based, and the alternative relative SST future Atlantic scenarios (graph 1a, and b respectively) provide different future Atlantic scenarios, and it is important to determine which of the two is most likely to occur (GFDL, 2018).

The most logical thing that a Geographer can do in such a scenario is to compare the existing records of the Atlantic hurricane frequencies, and intensities (1878 to present) in relation to the effects of global warming. At first glance, one will notice that there is an upward, and therefore positive trend between PDI, and the rising SSTs. However, it is important to take into consideration the methods that were used to collect data on hurricanes pre-1965- reports from ships (Goodwin & Donaho, 2010). If a researcher was to compare some of the modern era (post-1965) hurricanes hypothetically occurring in the earlier decades, it means that most of these tropical storms would not have been observed by the ship-based observing teams. Therefore, based on this notion by adjusting to include the hypothetical storms that may have been missed during the pre-1960 era, one notices only a small nominally positive upward trend in the tropical storm occurrence from 1878-2006. Furthermore, if an individual was to take into consideration only the hurricanes that have taken place in the Atlantic basin, rather than all the tropical storms the results are similar (Goodwin & Donaho, 2010). It is an indication that there is no significant positive trend between an increase in global warming to hurricane intensity, and frequency.

A detailed examination of the hurricane intensity from the 1970s shows that there has been a substantial change in relation to the intensity distribution of hurricanes globally. Although the number of category 1 hurricanes has remained constant during this period, it has decreased as a percentage of the total number of hurricanes that have occurred (Schwartz, 2015). Also, the sum of the categories 2 and 3 hurricanes is significantly small in number, and percentage. However, the category 4 and 5 hurricanes have doubled from 50% in 1970s to 90% in 2000s (Knutson & Tuleya, 2004). However, the increase of the category 4, and 5 hurricanes has not resulted in the increase of the intensity of these hurricanes. Although the increase in number, and intensity of the hurricanes has occasionally been attributed to global warming, experts point out that this period (1970-2000) is a limited time to conduct world climate research that can provide valid, and reliable results (Knutson & Tuleya, 2004).

Increased Population Leads to More Damages from a Hurricane

There is also the debate in relation to whether the increase in terms of the costs of damages by hurricanes are as a result of the increased...