PMM variability is not constant. Both the mean climate state—in particular the strength of the ocean surface heat flux variations caused by wind changes and the latitude of the ITCZ—and the storminess in the extratropics influence its variability. The ITCZ limits the extent of the PMM to the south, and fluctuations in the mean position of the ITCZ due to climate changes may thus impact the manifestation of the PMM. Simulations by Sanchez "et al." (2019) found increased PMM variability both in response to volcanic eruptions, such as the 1257 Samalas eruption and in response to greenhouse gases. Decreased PMM activity during the mid-Holocene may explain the weaker ENSO variability during that time; such a decrease might have been induced by orbital forcing. Bramante "et al." (2020) found positive PMM variations during the Medieval Climate Anomaly and negative PMM during the Little Ice Age and used it to explain changes in typhoon activity at Jaluit in the Marshall Islands and in the South China Sea.