With the news of another possible cyclonic storm near the Bengal delta, Biswasree asked if such storms can be generated or influenced by human activities. P.S.: You can also ask your question here "Are the causes of cyclones purely natural? Aren't there any anthropogenic reasons also?" Dear Biswasree, The formation of the cyclone is known as cyclogenesis. Everything about cyclogenesis is not known yet; there remain few open questions. Cyclogenesis has been occurring worldwide from the deep past, so it is not dependant on sapiens' (Human) existence. Hence, there is no anthropogenic cyclogenesis, and there will be no pure anthropogenic in the near future. Whether human activity can affect/modify cyclone, its formation, intensity, and track, remains a research challenge in climate science. It is difficult to answer it readily because it is complex at many levels. Human activity is clearly affecting large-scale climatic conditions. The Tropical Cyclone is, of course, dependant on these large-scale conditions, particularly the sea surface temperature (i.e., how hot the ocean water is) and the background wind. It is intuitive to think that human activity is affecting Tropical Cyclones somehow, but quantification is challenging. For example, due to the emission of greenhouse gases, our planet is warming, including the ocean waters. Increasing moisture supply from warming oceans may result into more frequent and stronger cyclones when other conditions are favorable. The figure below shows the rise in ocean temperature in the last 117 years. Such a rise of temperature of more than 1 degree c may indeed affect the strength/ frequency of Tropical Cyclones but, the exact percentage of the human influence is difficult to answer. What does that last statement mean? Let us take an example. There may be all favourable conditions in a particular situation to form a cyclone, except the sea surface temperature , which is 0.5 degree less than needed. In this condition, the cyclone can not form. Now, if the anthropogenic effect causes the sea temperature to rise by 0.6 degree, cyclogenesis will be possible. However, this cyclogenesis cannot be termed purely anthropogenic, as other conditions that make the genesis possible are not human-influenced. Nevertheless, of course, human influence is necessary for the genesis in this particular example. Similarly, anthropogenic aerosol can affect the cloud systems of Tropical Cyclones . So, in theory, there are chances that humans can affect Tropical Cyclones some way or other, but there is no complete quantification yet. Some model experiments are conducted under the jurisdiction of the Intergovernmental Panel on Climate Change (IPCC) [1, 2]. Models found that warming scenarios might significantly change the cyclone frequency/intensity/movement in some locations. Also, few studies have shown that there will be significant changes in large-scale climatic features in future warming scenarios, which indeed affects Tropical Cyclone frequency and intensity. If the warming trend continues in the future, there might be some quantifiable influence. So, there are clear possibilities. Until now, no clear trend is reflected from the data that cyclone frequency is increasing. There are few claims about increase in cyclone intensity in recent times , but, there is not enough data to reach a consensus yet. This link can be of interest, where one of the leading Tropical Cyclone experts in the World, Kerry Emmanuel, answered some FAQs, https://emanuel.mit.edu/anthropogenic-effects-tropical-cyclone-activity Notes: [1] https://pcmdi.llnl.gov/mips/cmip5/ [2] How humans can affect the strength of tropical cyclones This answer given by our team member Sambrita.
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