Editing IPCC:AR6/WGI/Chapter-11 (section)

==== 11.7.1.1 Mechanisms and Drivers ====

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The genesis, development, and tracks of TCs depend on conditions of the larger-scale circulations of the atmosphere and ocean ( [[#Christensen--2013|Christensen et al., 2013]] ). Large-scale atmospheric circulations, such as the Hadley and Walker circulations and the monsoon circulations can significantly affect TCs, as can internal variability acting on various time scales (Annex IV), from intra-seasonal (e.g., the Madden–Julian and Boreal Summer Intraseasonal oscillations and equatorial waves) and interannual (e.g., the El Niño–Southern Oscillation and Pacific and Atlantic Meridional Modes), to inter-decadal (e.g., Atlantic Multidecadal Variability and Pacific Decadal Variability). This broad range of natural variability makes detection of anthropogenic effects difficult, and uncertainties in the projected changes of these modes of variability increase uncertainty in the projected changes in TC activity. Aerosol forcing also affects sea surface temperature (SST) patterns and cloud microphysics, and it is ''likely'' that observed changes in TC activity are partly caused by changes in aerosol forcing ( [[#Evan--2011|Evan et al., 2011]] ; [[#Ting--2015|Ting et al., 2015]] ; [[#Sobel--2016|Sobel et al., 2016]] , 2019; [[#Takahashi--2017|Takahashi et al., 2017]] ; [[#Zhao--2018|Zhao et al., 2018]] ; [[#Reed--2019|Reed et al., 2019]] ). Among possible changes from these drivers, there is ''medium confidence'' that the Hadley cell has widened and will continue to widen in the future (Sections 2.3, 3.3 and 4.5). This ''likely'' causes latitudinal shifts of TC tracks ( [[#Sharmila--2018|Sharmila and Walsh, 2018]] ). Regional TC activity changes are also strongly affected by projected changes in SST warming patterns ( [[#Yoshida--2017|Yoshida et al., 2017]] ), which are highly uncertain (Chapters 4 and 9).

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