Climate change affects tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, an increase in the frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the consequences of human-induced climate change.[1][2] Tropical cyclones use warm, moist air as their source of energy or fuel. As climate change is warming ocean temperatures, there is potentially more of this fuel available.[3]
Between 1979 and 2017, there was a global increase in the proportion of tropical cyclones of Category 3 and higher on the Saffir–Simpson scale. The trend was most clear in the north Indian Ocean,[4][5]North Atlantic and in the Southern Indian Ocean. In the north Indian Ocean, particularly the Arabian Sea, the frequency, duration, and intensity of cyclones have increased significantly. There has been a 52% increase in the number of cyclones in the Arabian Sea, while the number of very severe cyclones have increased by 150%, during 1982–2019. Meanwhile, the total duration of cyclones in the Arabian Sea has increased by 80% while that of very severe cyclones has increased by 260%.[4] In the North Pacific, tropical cyclones have been moving poleward into colder waters and there was no increase in intensity over this period.[6] With 2 °C (3.6 °F) warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength.[1] A 2019 study indicates that climate change has been driving the observed trend of rapid intensification of tropical cyclones in the Atlantic basin. Rapidly intensifying cyclones are hard to forecast and therefore pose additional risk to coastal communities.[7]
Warmer air can hold more water vapor: the theoretical maximum water vapor content is given by the Clausius–Clapeyron relation, which yields ≈7% increase in water vapor in the atmosphere per 1 °C (1.8 °F) warming.[8][9] All models that were assessed in a 2019 review paper show a future increase of rainfall rates.[1] Additional sea level rise will increase storm surge levels.[10][11] It is plausible that extreme wind waves see an increase as a consequence of changes in tropical cyclones, further exacerbating storm surge dangers to coastal communities.[12] The compounding effects from floods, storm surge, and terrestrial flooding (rivers) are projected to increase due to global warming.[11]
There is currently no consensus on how climate change will affect the overall frequency of tropical cyclones.[1] A majority of climate models show a decreased frequency in future projections.[12] For instance, a 2020 paper comparing nine high-resolution climate models found robust decreases in frequency in the Southern Indian Ocean and the Southern Hemisphere more generally, while finding mixed signals for Northern Hemisphere tropical cyclones.[13] Observations have shown little change in the overall frequency of tropical cyclones worldwide,[14] with increased frequency in the North Atlantic and central Pacific, and significant decreases in the southern Indian Ocean and western North Pacific.[15] There has been a poleward expansion of the latitude at which the maximum intensity of tropical cyclones occurs, which may be associated with climate change.[16] In the North Pacific, there may also have been an eastward expansion.[10] Between 1949 and 2016, there was a slowdown in tropical cyclone translation speeds. It is unclear still to what extent this can be attributed to climate change: climate models do not all show this feature.[12]
^Collins, M.; Sutherland, M.; Bouwer, L.; Cheong, S.-M.; et al. (2019). "Chapter 6: Extremes, Abrupt Changes and Managing Risks"(PDF). IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. p. 602. Archived(PDF) from the original on December 20, 2019. Retrieved October 6, 2020.
^ abCollins, M.; Sutherland, M.; Bouwer, L.; Cheong, S.-M.; et al. (2019). "Chapter 6: Extremes, Abrupt Changes and Managing Risks"(PDF). IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. p. 603. Archived(PDF) from the original on December 20, 2019. Retrieved October 6, 2020.