ESSEA Final Project part 2 - CSA

Causal Chains

1. E > A > B

A hurricane is often accompanied by a phenomenon known as a “storm surge.” The winds of a hurricane tend to be most intense in the right-forward quadrant of the storm. This is a result of adding together the speed and direction of the winds associated with the hurricanes: the movement of the storm itself over the earth, and the spiraling-inward winds. When these two motions are in the same direction, their wind speeds add together, reinforcing each other. This combined wind can push a large amount of water onshore and cause extensive wind damage to structures and life along the coast.

When a hurricane is out in the open ocean, the ocean’s surface bulges upward a bit – a few feet – under the eye of the hurricane because of the lower atmospheric pressure within the eye of the storm. This bulge increases in height as it comes into progressively shallower water much as any ocean wave gains height as it enters shallower water. The storm surge is often the most damaging aspect of the hurricane, producing massive and sustained flooding over a wide area and impacting animal and plant life.

2. E > A > E > A > . . .
Hurricanes transfer large amounts of energy, heat and moisture from the ocean into the atmosphere.
http://www.sciencedaily.com/releases/2005/01/050110114115.htm
The temperature of a substance is a relative measure of the average kinetic energy of the particles within the substance. Thus, water at 30^oC will have a normalized distribution of slow, average, and fast particles. These faster particles can attain enough energy to escape the liquid state completely and evaporate. Of course, as the temperature of the substance increases, more particles will gain enough energy to escape into the vapor stage.
Normally, this evaporation – escape of higher-energy water particles – results in lowering the average kinetic energy of the particles left behind in the liquid state. Hence, the phenomenon of evaporative cooling. Effectively, the water vapor has carried some of the energy from the ocean into the atmosphere.
As the mass of air containing this water vapor rises into the atmosphere, it undergoes expansion as it encounters the decreasing atmospheric pressure at higher altitudes. As the air mass expands, it cools, and the water vapor condenses back into the liquid state. Each kilogram of water that condenses releases 3.30 x 10⁵ J back into the atmosphere – almost 80 times the amount of energy required to change the temperature of that one kilogram of water by 1^oC. This relatively massive amount of energy is released into the surrounding atmosphere and tends to add energy to the ocean surface below, resulting in increased evaporation rates.. This energy also causes increased wind speed, which encourages further evaporation from the surface by breaking the surface into smaller droplets. Increased evaporation carries more energy into the atmosphere, releasing more energy as the latent heat of condensation. The hurricane acts as a system in resonance with each event reinforcing the effects of the other events.

3. E > H > A

When wind speeds increase, ocean turbulence increases, resulting in greater rates of evaporation from the ocean surface. As wind speed increases, the amount of ocean spray increases; this spray is simply the ocean surface broken up into smaller volumes. As the surface area of a given mass of water increases, it becomes more likely that water particles can escape the liquid state because they’re now nearer the surface of the water.

For example, one cubic meter of water measures 1 m x 1 m x 1 m. The surface of this cubic meter of water is 6 x (1 m x 1 m) = 6 m² of surface area. On the other hand, if this much water is broken up into cubic centimeters, there will be (100 cm x 100 cm x 100 cm) = 10⁶ cm³ of water. The surface area for each of these tiny packages of water is 6 x (10^-2 m x 10^-2 m) = 6 x 10^-4 m². Multiply this surface area per cm³ by 10⁶ of these cubes, and there are 6 x 10² m² of surface area – 100 times as much surface area, and now the same number of water particles (remember, the mass of water didn’t change, it was just re-packaged) will be much closer to the surface and more likely to be evaporated.

4. E>B>A>H

High wind speeds produce large ocean waves, which in turn can damage the framework of coral reefs. The amount of damage to massive corals is slight, but more delicate coral structures can face 99% damage.
http://www.int-res.com/articles/meps/78/m078p201.pdf

Coral reefs act as large carbon sinks. As coral reefs are destroyed, less carbon can be stored in the ocean and more is available to the atmosphere, resulting in increased concentrations of CO₂ and increased atmospheric temperatures. These increased atmospheric temperatures result in increased ocean temperatures, which may increase the intensity of hurricanes.

5. E > B > A

53% of the US population and 55% of the world’s population lives within 50 miles of a coastline. This increase in development and property values means that even if hurricanes do not change in frequency or intensity, we still face horrific costs with each successive hurricane. Low-lying, developing countries such as Bangladesh and India face increased risk of large numbers of human fatalities if there’s an increase in hurricane frequency or intensity.
http://www.noaanews.noaa.gov/stories2007/s2811.htm ; http://www8.nos.noaa.gov/nccos/npe/projectdetail.aspx?id=61&fy=2007

When nations must be concerned more about protecting their citizens from imminent and frequent flooding, they will be less concerned with regulating their carbon emissions.

6. E > B > B

A hurricane can strip coastal forests of branches and leaves, uproot trees with weak root systems, and the resulting leaf litter on the forest floor can choke out the undergrowth. The torrential rainfall can produce mudslides which in turn devastate an area’s ecology. Water left standing can contribute to increased mosquito populations and the accompanying malaria & dengue fever.
http://emissionhq.com/2weeks/hitsPuertoRico.aspx

DDT is still the insecticide of choice (National Geographic, August 2007) for eradicating malaria-bearing mosquitoes. If nations use more DDT, the biosphere will undergo other changes in the quantity and quality of its waterfowl a la Rachel Carson’s “Silent Spring.”

7. B > E > A > H

In the past, coastal wetlands have served as buffers between hurricanes and populated areas. With the coastal wetlands disappearing at a rate (in Louisiana) of 25 square miles per year, populated areas will see more damage and fatalities from hurricanes even if the intensity and frequency of hurricanes does not increase.
http://www.washingtonpost.com/wp-dyn/content/article/2005/11/10/AR2005111000138_pf.html

Likewise, as wetlands are replaced with developments, an area loses its capability for carbon sequestration. This lack can lead to increased concentrations of CO₂ in the atmosphere, resulting in increased global temperatures in the atmosphere and then in the oceans. These increased temperatures could help increase the intensity of hurricanes.

8. H > L > B

Rainfall causes increased water flow resulting in increased erosion. In turn, this leads to greater sediment levels in the rivers which are deposited as the velocity of the water decreases downstream. The good news is that this increased sediment load can help buoy up sinking river deltas. On the other hand, the Mississippi’s sediment load has decreased by 25% over the past several decades, and the Mississippi River delta – upon which the city of New Orleans is located – is sinking as a result. This in turn leads to the potential for more damage from the storm surges that accompany hurricanes.

9. L > A > L > A . . .
Eroded, barren land can give up more dust into the atmosphere, providing more condensation nuclei for water vapor. Greater precipitation over these areas will result in even more erosion, exacerbating the problem.

10. H > A > H > A . . .

The warm ocean water provides water vapor to the atmosphere, and its condensation provides energy for further evaporation of water from the ocean surface. This feedback loop, aided by lack of wind shear in the upper atmosphere, provides the impetus for hurricane formation and intensification.