Tropical Cyclones in a Warmer World
Tropical cyclones (hurricanes and typhoons) generate serious costs to human life, property, and the economy. Understanding how the behavior of tropical cyclones may change in a warmer climate is important for long-range coastal planning and infrastructure investments to minimize impacts. To help address this prediction challenge, NASA, NOAA, NSF, and DOE have cosponsored a Hurricane Working Group (HWG), organized through the interagency U.S. Climate Variability and Predictability (US CLIVAR) Program and composed of leading hurricane scientists and climate modelers from the United States and abroad. The HWG recently coordinated a set of experiments using seven atmospheric models to examine how the frequency of tropical cyclones may respond to future changes in the ocean–atmosphere system.
Though results varied somewhat from model to model, all of the models predicted a global decrease in tropical cyclone frequency in response to increases in both atmospheric carbon dioxide concentrations and sea surface temperatures. Regional differences were evident among ocean basins, with large decreases predicted in the frequency of tropical cyclones in the western Pacific and Indian Oceans, and smaller magnitude changes—both increases and decreases in frequency—in the Atlantic Ocean. These experiments build on a larger body of work that suggests that overall, tropical cyclones will occur less frequently as climate change progresses. However, the best-available science also projects an increase in the annual number of the strongest (Category 4 and 5) hurricanes, as well as increases in tropical cyclone intensity and rainfall rates. Although they may occur less frequently, future storms that make landfall (even at today’s intensity levels) are likely to have increasingly destructive effects as a result of rising sea levels.
This map shows projected changes in the annual frequency of tropical cyclone formation, averaged from the output of seven models, under the combined conditions of 1) a 2°C increase in sea surface temperatures, and 2) a doubling of atmospheric carbon dioxide concentrations relative to the present day. Dots denote areas where at least five of the seven models agree on the direction (increase or decrease) of the change in frequency. Although localized increases are projected, the models point to an overall global decrease in the formation of tropical cyclones. (Source: Zhao et al., 2013)