The Connection Between the North and South American Monsoons

We review evidence for a potential link between the North American Monsoon (NAM) and the South American Monsoon (SAM). Such a link is poorly documented in the literature, but if it were to exist, it could involve the influence of a monsoon onset on the cross-equatorial flow, atmospheric wave responses, and oceanic feedback to monsoon heating anomalies, which could in turn influence the decaying monsoon. With such a link, the variability of the NAM demise could be influenced by that of the SAM onset (or vice versa), in addition to its known dependence on regional land surface and adjacent oceans. The historical correlation between the NAM and the SAM appears to be mainly a consequence of both being dependent on tropical oceanic variability, such as El Niño-Southern Oscillation (ENSO), but an inter-monsoon link could be important for understanding the future climate variability of the American monsoons when the effects of anthropogenic forced change become more dominant—e.g., through reduction of evapotranspiration (ET) due to CO2 fertilization of the rainforest and large-scale land use over the Amazon. These effects might perhaps not only delay the onset of the SAM, but also impact the demise of the NAM.