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Are Irma and Harvey a Product of Global Warming?

     A lot of focus has been on the hurricanes hitting the southeast United States this year. Hurricane Harvey devastated much of Texas and Hurricane Irma flooded parts of Florida. Additionally, there have also been multiple other hurricanes and tropical storms this season that did not receive as much press. Irma and Harvey were both touted by the news as “once in a century storms”. What are the chances of two storms of this magnitude hitting together? Many have proposed that climate change is causing the strong influx of hurricanes this season. Is that possible?

To understand the effects of climate on hurricane strength, it is important to understand how a hurricane forms. The word hurricane specifically refers to a tropical cyclone formed in the tropical Pacific or Atlantic waters. A specific set of requirements must be met for a hurricane to form. First off, the storm must begin at least 300 miles from the equator. The spinning of the earth causes an effect called the Coriolis force. This force is what causes the winds to spin. When the storm is too close to the equator, winds will not spin and a hurricane cannot form. The surface temperature of the water in which the hurricane forms must be at least 80 degrees Fahrenheit with the air above having to be significantly cooler. Moist air makes the creation of a hurricane smoother as well. This is because hurricanes “feed” off the heat energy of the convection in these temperature differences. When winds blow against the warm water, it rises and cools to water droplets in the atmosphere. This forms the thunderclouds that are necessary for a hurricane.

This group of thunderclouds travel across the ocean. For a hurricane to form, these clouds must encounter an area of low pressure called a tropical disturbance. In this area, winds blow towards each other which causes air to rise. With the right hurricane-seeding conditions, a spinning column of air called the mesoscale convective vortex will form. As winds travel up this vortex, they are carrying ever cooling molecules of air. When the molecules finish cooling at the top of the vortex, they release energy and warm the air near the top of the column. In turn, this creates an area of high pressure at the top of the vortex and an area of low pressure at the bottom of the vortex. Winds will move away from the area of high pressure and towards the area of low pressure at the bottom forming a circular pattern of winds. This cycle will build upon itself, creating more thunderstorms and higher velocity winds. At wind speeds of 39 mph, the storm is officially a tropical storm and at wind speeds of 74 mph, the storm is a hurricane.

Tracking hurricane trends is difficult. Reporting on these storms is much more accurate today with satellite imaging than it was in the past, so making century long comparisons is difficult. There seems to be no significant increase in the number of hurricanes in the past 100 years when likely missed storms are taken into account, but the number of severe storms has increased dramatically. From 1975 to 2004, the number of category 4 and 5 hurricanes almost doubled.

Climate change can influence the effects of hurricanes in multiple ways. Since hurricanes feed off the warm waters, global warming can affect the intensity and quantity of hurricanes. The rise in sea surface temperatures gives a greater area where hurricane formation can take place. According to one study, the wind speed of hurricanes will increase 2-11% by 2100 and the frequency of storms by 6-34%. Rainfall is also expected to increase about 20% for areas near the storm’s eye. However since hurricane formation is complicated and relies on many elements, some future models differ from this prediction. However, the general consensus among models is that the number of extremely strong storms will increase. Additionally, rising sea levels from glacier melting and shore erosion can lead to the potential for greater property damage during storms. While these predictions are not certain, it is clear that the increase in water temperatures can potentially harm people living on the shoreline.

Read about hurricane formation here

Read about the effects of global warming on hurricane development here

Edited By: Briana Fannin