This video segment adapted from NOVA scienceNOW highlights research that supports the idea that warmer oceans generate and sustain more intense hurricanes. Ongoing monitoring of sea surface temperature (SST) has supplied evidence that the world's oceans warmed 0.5°C between 1970 and 2005. Because hurricanes rely on warm seawater to release heat into the upper atmosphere and create spiraling winds, any additional energy can result in increased intensity. The video examines factors scientists use to predict hurricane behavior, and states that the complex nature of hurricane formation makes predicting with a high degree of accuracy very difficult.
Until fairly recently, most scientists denied that global climate change and hurricane activity were related in any way. They said that hurricanes were subject to a separate cycle of oceanic and atmospheric activity that seemed to shift every 25 years or so. However, an increasing body of evidence now suggests that hurricane intensity—a measure of strength—is directly linked to rising global temperatures.
A hurricane begins when winds blowing across the surface of warm ocean water converge to form clusters of strong thunderstorms known as tropical disturbances. The heat of the water provides the energy these tropical storms need to build. As they do, water evaporates from the ocean surface and enters the air as water vapor. As the vapor rises and cools, it condenses and forms clouds, a process that releases heat. The heat warms the center, or eye, of the storm, which in turn causes more water to evaporate. Meteorologists call this cycle a "heat engine." As long as a storm has access to warm ocean water, this engine will continue to drive the storm's growth.
Since 1970, climate scientists have noted a gradual warming of the world's oceans. Most attribute this warming to an increase in greenhouse gas concentration in the atmosphere. In trying to determine whether there is a definitive link between rising sea surface temperature (SST) and hurricane intensity, scientists have noted that a 0.5ºC rise in global SST between 1970 and 2005 resulted in a 4 percent increase in atmospheric water vapor. Again, water vapor is associated with producing larger and more powerful hurricanes, so there may be a connection.
The Saffir–Simpson Hurricane Scale is used to classify hurricanes according to their intensity level. In order to be classified as a Category 1 hurricane, a tropical cyclone must have maximum sustained winds of at least 119 kilometers (74 miles) per hour. The highest classification on the scale, Category 5, is reserved for storms with winds exceeding 249 kilometers (155 miles) per hour. The classifications are intended primarily for use in measuring the potential damage and flooding a hurricane will cause upon landfall.
Scientists are under a lot of pressure to accurately predict hurricane direction and intensity. As Hurricane Katrina—a Category 4 storm that inundated New Orleans and nearby coastal areas in 2005—demonstrated, lives and property are at risk. While scientists have gotten pretty good at predicting the direction of a hurricane, they are not as good at predicting intensity. This is largely because they lack tools that enable them to read all the changes in terrain and water temperature that might cause a hurricane to strengthen or weaken. Using satellites equipped with weather radar, they are beginning to better visualize the internal structure of hurricanes. This may enable them to detect signs that a hurricane is about to enter an intensification phase, which can aid hurricane preparedness.
Here are suggested ways to engage students with this video and with activities related to this topic.
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