Short answers, pulled from the story.
The Atlantic Multidecadal Oscillation (AMO), also called Atlantic Multidecadal Variability (AMV), is the theorized variability of sea surface temperatures in the North Atlantic Ocean over timescales of several decades. It describes slow cycles of warming and cooling that appear to repeat roughly every 70 years based on about 150 years of instrument records.
Climate scientist Michael Mann coined the term 'Atlantic Multidecadal Oscillation' during a 2000 telephone interview with journalist Richard Kerr, as Mann described on page 30 of his 2012 book The Hockey Stick and the Climate Wars: Dispatches from the Front Lines.
During warm AMO phases, at least twice as many tropical storms can mature into severe hurricanes compared with cool phases. However, researchers including Mann and Emanuel argued in 2006 that long-term trends in hurricane activity are driven by anthropogenic warming rather than the AMO.
The AMO is correlated with summer temperatures and rainfall across much of the Northern Hemisphere. Warm AMO phases are linked to more frequent droughts in the US Midwest and Southwest, stronger summer rainfall over India and the Sahel, more Atlantic hurricane activity, and changes in spring snowfall over the Alps. Florida and the Pacific Northwest tend to see more rainfall during warm AMO phases.
Instrument records only span roughly 130 to 150 years, providing too few data points for reliable statistical forecasting. No deterministic method has demonstrated an ability to predict when the AMO will shift phase. Enfield and Cid-Serrano used a 424-year proxy reconstruction and found that about 70 percent of regime shifts occur within 20-year windows, but timing a specific shift remains beyond current models.
No. There is ongoing scientific controversy over whether the AMO represents a genuine internal ocean oscillation or an artifact of how global warming signals are removed from the data. A 2021 study by Michael Mann and colleagues argued that the apparent periodicity was driven by volcanic eruptions and external forcings, and that the AMV signal is statistically indistinguishable from red noise.