Hurricanes are driven by a thing called “Thermodynamic Disequilibrium”. In order to attain “Thermodynamic Equilibrium” , three different types of equilibrium must happen; 1.) Thermal Equilibrium 2.) Mechanical Equilibrium and 3.) Chemical Equilibrium. 

Thermal Equilibrium is when the system does not change with time and has the same value in all locations of the system. This means that the temperature does not change anywhere in the system of the storm. Hurricanes have a gradient in temperature from the outer bands to the eye from warm to cold.

Mechanical Equilibrium is when the geostrophic winds are in balance within and around the system. This means that the Pressure Gradient Force (PGF), Coriolis Force, and Frictional Force are all in balance. Since we’re talking about a system that is located in the upper atmosphere, friction does not exist. Hurricanes have different forced winds in every location of the system therefore this part would not make any sense.

Finally, there is the Chemical Equilibrium. This is when there is no chemical reaction present in the system and every location in the system has the same chemical composition. Between the many different unstable forms within a hurricane, there’s no way for the atmospheric chemicals to be in balance.

This Disequilibrium drives a strong flow of heat from the ocean to the atmosphere. This is a direct consequence from the Greenhouse Effect. To explain the Greenhouse Effect, it is simply the rise in global temperatures caused by the pollutants in the the air like carbon dioxide, methane, and chlorofluorocarbons. It tends to focus its effects on the regions where it was created. Carbon Dioxide (CO2) is the biggest contributor to the Greenhouse Effect and is the largest presence of any human-produced Greenhouse Gas. Tiny island nations are the most vulnerable to these gases because of Sea Level Rise.

Some examples of how Climate Change effects hurricanes are Katrina and Sandy. Both of these systems were present during a strong El Nino season. 

 Hurricane Katrina made landfall in Louisiana as a category 3 and caused storm surges as high as 27 feet tall. She was the third largest hurricane to make landfall in the United States and caused an estimated $14 billion in damage. 1,200+ people lost their lives to this storm and caused 80% of New Orleans to be submerged in water. Some news companies went as far to say that Hurricane Katrina should have been nicknamed “Climate Change Herself” because of the pure  shock and devastation that she brought to New Orleans.

Superstorm Sandy was another devastating storm. She was a Category 1 when she made landfall in the Caribbean and Haiti but then when heading up the East coast of the United States, lost her intensity and made landfall in New Jersey and New York as a tropical storm with sustained wind speeds of 70mph. Only 149 deaths were caused by this system (most from the Caribbean and Haiti).

The Terrible Trio of 2005

Hurricane Katrina was part of something called the “Trio of 2005” which involved 3 different systems that were devastating and dangerous to the United States and surrounding islands. The other two hurricanes involved were Wilma and Rita. 

Katrina and Rita both reached a category 5 by passing over a patch in the central Gulf of Mexico heated by an infusion of deep, warm water from the Caribbean. This is caused by the Loop Current. By the time they made landfall, both were a category 3.

Wilma intensified from a category 1 to the lowest barometric pressure recorded within a 12 hour period of 882 hectopascals. 

The Triple Whammy: Harvey, Irma, and Maria

Hurricane Harvey made landfall in Texas as a category 1 on August 25th, 2017. 30,000 people living in Texas fled to temporary shelters before and stayed after the storm until their houses could be rebuilt (if that was even possible).  The death toll was 88 people, all being people that did not decide to evacuate from the coast. In total over 50 inches of rain was reported and the storm caused approximately $125 billion in damage.

Hurricane Irma first made landfall as a category 4 on the islands of Antigua and Barbuda leaving it barely habitable. Next it moved onto Puerto Rico, Haiti,Dominican Republic, Caicos islands, and the Bahamas (also as a category 4) with over 15 inches of rain and severe flooding. When Irma downgraded to a category 3, she affected the North-East of Cuba and Havana with waves up to 36 feet high. Upgrading again to a category 4 she hit the Florida Keys with 12 inches of rain and Miami reached a state of emergency.

Hurricane Maria was developed less than two weeks later and intensified all the way to a category 5 with sustained winds of 175mph. The Dominican Republic and Puerto Rico were the worst affected. This led to Puerto Rico asking neighboring countries for $94 billion to cover the damages. The United States made a donation of $24 million.

Will there be more cyclones in the future?

Peter Webster (Georgia Institute of Technology) led a team ranking cyclones since the 1970s to find a pattern in intensity. He discovered that the strongest cyclones were nearly 50% more frequent globally from 1990-2004 than they were from 1975-1989. From his work, we can see that sea surface temperatures in the North Atlantic alternated every 30-40 years from warming to cooling. He came to the conclusion that tropical cyclones might get larger over time in some areas but results varied by region.

Sources:

“Global Warming and Hurricanes.” GFDL, http://www.gfdl.noaa.gov/global-warming-and-hurricanes/.

Leslie, Jacques, et al. “Atlantic Hurricanes Are Becoming Stronger Faster, Largely Due to Climate Change.” Yale E360, 8 Feb. 2019, e360.yale.edu/digest/atlantic-hurricanes-are-becoming-stronger-faster-largely-due-to-climate-change.