About 20 years ago, through the course of their research, Michael Mann — distinguished professor of atmospheric science at Pennsylvania State University — and his colleagues identified a novel phenomenon. //
About every half-century, wind and waves seemed to conspire to warm up or cool down part of the North Atlantic, with probable large-scale effects on weather.
Drawing on the same Earth simulations on which most climate research was then based, they concluded that the back-and-forth swing must be a feature intrinsic to the natural system itself. Mann dubbed it the “Atlantic Multidecadal Oscillation” (AMO). //
Only here’s the thing: The Atlantic Multidecadal Oscillation turns out not to actually exist. That’s the latest and definitive conclusion from Mann and three colleagues, who wrote recently in the journal Science that the newest climate models can no longer find any evidence of a natural temperature flip in the Atlantic every few decades.
Instead, the data has led them to another smoking gun: smoking volcanoes.
Research into ancient climates suggests that before industrialization took off in the 19th century, volcanoes periodically belched out enough sulfate aerosols to explain the “oscillation” going back a thousand years. These aerosols have a cooling effect, by reflecting about a quarter of sunlight back into space, until they wash out of the atmosphere within months or a few years.
In the 20th century, the steady concoction of man-made warming and cooling pollution likely influenced the temperature swings.
“This article is the final nail in the coffin,” said Mann, who last month chronicled his experiences bringing climate science into the public sphere in a book, The New Climate War.
