Hurricanes and Climate Change

Hurricanes are dynamic storm systems whose intensities are governed by the interactions between the storm, underlying ocean, atmospheric environment, and internal physical processes. Following the influx of damaging hurricanes in 2005, more research was implemented to discover correlations between climate change and increased cyclone severity. Though climate change deniers may attempt to confuse these findings, the data stands to measure that climate change does directly affect the severity of tropical cyclones through its effects on sea surface temperature.

Tropical cyclones form due to atmospheric disturbances in or near a tropical ocean coupled with warm water temperatures and favorable atmospheric conditions with high moisture and low wind shear.

Categorization of tropical storms is typically based on wind speed which acts as a direct measure of storm intensity. Hurricanes are categorized 1 through 5 with category 1 being the least intense with the weakest winds while category 5 is the most intense and has the highest wind speeds. Storm categories 3 through 5 are all considered to be major damaging storms.

Tropical sea surface temperature has direct influence on the development of hurricane intensity. This relationship was discovered over 50 years ago, when it was observed that tropical cyclones do not form unless the underlying SST exceeds the temperature threshold of 26.5°C. It is also well documented that warm sea surface temperatures act to supply energy for the development of hurricane winds. As the tropical SST continues to increase, it surpasses the temperature threshold for cyclone development and provides more and more energy for the developing system, leading to stronger winds and an overall higher measured intensity than previously expected without said increase in sea surface temperature.

Global warming has direct influence on SST. As the trapped greenhouse gases continue to reflect and intensity radiation from the sun, they warm the entire planet, leading to an increase in air and ocean temperatures. According to the Intergovernmental Panel on Climate Change (IPCC), global SST is expected to rise by approximately 0.4 – 1.1°C by 2025. This unprecedented warming will increase ocean thermal energy which in turn will increase the severity of developing hurricanes. Though it can be dangerous to imply direct causation from statistical correlation, if the correlation is intense enough it implies a common cause or relationship. When considering data collected over the last fifty years, a time period in which SST increased globally by an average of 0.17 ? per decade, this relationship reveals itself. Since 1970, though the total number of hurricanes has not increased globally, the proportion of category-4 and -5 hurricanes has doubled, implying that the distribution of hurricane intensity has shifted to being more intense due to factors such as climate change which are increasing the amount of available energy for developing storm systems.

Amount of rainfall is also an important variable when considering the relationship between global warming and the intensity of hurricanes. Cyclones on average globally produce and deposit between 6-12 inches of rainfall per storm cycle. As the climate warms this number is expected to increase as warmer air can hold more moisture and produce more rain. This expected increase in rainfall follows the Clausius-Clapeyron equation, which dictates that for every one degree Celsius increase in temperature, atmospheric air can hold up to 7% more moisture. According to the National Oceanic and Atmospheric Administration (NOAA), current modeling studies project an estimated 10-15% increase in rainfall rates associated with hurricane weather systems, for a 2 degree Celsius increase global warming situation. Since 1900 the world has experienced warming of about 1 ? due to climate change, with most of the warming occuring after the 1970’s. As of 2017, Hurricane Harvey had an estimated 15% greater rainfall average than other hurricanes which dated to the 1950’s. Hurricane rainfall rates are likely to continue to increase in the future due to global warming and its accompanying increase in atmospheric moisture content.

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