Hurricanes form in the tropics over the ocean where the sea surface is warm and so is the air. They go by different names in different places – like tropical cyclones and typhoons. Scientists use the Saffir-Simpson scale to describe the strength of hurricanes (Category 1-5). Hurricanes form in areas of low pressure over a large area of warm water. Air is drawn into the low pressure in a spiral pattern due to the Coriolis effect. Hurricanes draw energy from the warm water they move over.
Scientists have determined that the strength and length of storms are probably affected by climate change. There is evidence that the number of hurricanes during each season changes over time with a natural cycle and may not be directly affected by climate warming.
As climate warming causes the ocean surface to warm, the intensity of hurricanes will likely increase. Hurricanes take heat energy from the oceans and convert it into the energy of the storm. Thus, warmer oceans offer more heat energy to hurricanes, allowing them to become stronger storms with higher winds. Also, as climate warms hurricanes are able to transport more moisture, which can cause intense precipitation and devastating floods and damage, like those that occurred with Hurricane Harvey in the Houston, Texas area in 2017.
In the final part of this activity, students compare hurricane data from three time periods to explore whether there is a trend in the number of strong hurricanes (using a method similar to Webster et al., 2005). Students observe that there is evidence that storms are becoming stronger but also note that the trend isn't as clear in all regions. This is an area of active research and scientists are currently trying to learn more about the connection between warming and strong hurricanes. There is strong evidence that recent climate change caused by humans has been increasing the intensity of hurricanes.
- For more information, see Webster et al., 2005, Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment. Science 309, 1844-46.
- If you would like students to look at the Map of Tropical Cyclone paths (1985-2005) in more detail, download the Wikimedia high-resolution version.
This activity was developed by Lisa S. Gardiner for NESTA in 2006 and revised for the UCAR Center for Science Education in 2018.