Michael Mann coined the term Atlantic Multidecadal Oscillation during a telephone interview with Richard Kerr in 2000. He later recounted this moment in his book The Hockey Stick and the Climate Wars published in 2012.
Rainfall patterns shift significantly in Northeastern Brazil and the African Sahel region when the cycle changes. Warm phases of the AMO increase the frequency or duration of droughts in the US Midwest and Southwest while climate models show warm AMO phases strengthen summer rainfall over India and the Sahel. Paleoclimatologic studies confirm increased rainfall during warm phases and decreased rain during cold phases for the Sahel over three thousand years.
Meteorological science indicates many more tropical storms mature into severe hurricanes during warm AMO phases than during cool ones. At least twice as many severe hurricanes form during warm periods compared to cold periods. Enfield and colleagues assumed the current warm regime would persist until at least 2015 and possibly as late as 2035.
A 2021 study by Michael Mann and others showed periodicity in the last millennium was driven by volcanic eruptions and external forcings. They found no compelling evidence supporting the existence of the AMO as a true oscillation or cycle because models displayed no oscillatory behavior on timescales longer than the El Niño Southern Oscillation phenomenon. The Atlantic Multidecadal Variability became indistinguishable from red noise which serves as a typical null hypothesis for testing oscillations.
Only about 130 to 150 years of instrument-based data exist for analyzing this climate pattern. These samples are too few for conventional statistical approaches to yield reliable results so researchers used multi-century proxy reconstructions to extend analysis to 424 years.