Humans held responsible for twists and turns of climate change since 1900

https://www.sciencemag.org/news/2019/05/humans-held-responsible-twists-and-turns-climate-change-1900

Source: By Paul Voosen, Science Magazine. 

Excerpt: While industry and agriculture belched greenhouse gases at an increasing pace through the 20th century, global temperature followed a jagged course, surging for 3 decades starting in 1915, leveling off from the 1950s to the late 1970s, and then resuming its climb. For decades, scientists have chalked up these early swings to the planet’s internal variability—in particular, a climatic pacemaker called the Atlantic Multidecadal Oscillation (AMO), which is characterized by long-term shifts in ocean temperatures. But researchers are increasingly questioning whether the AMO played the dominant role once thought. The oceanic pacemaker seems to be fluttering. It is now possible to explain the record’s twists and turns almost entirely without the AMO, says Karsten Haustein, a climate scientist at the University of Oxford in the United Kingdom and lead author of a new study published this month in the Journal of Climate. ... “It’s very unlikely there’s this ocean leprechaun that produces cyclicity that we don’t know about,” Haustein says—which means it is also unlikely that a future cool swing in the AMO will blunt the ongoing human-driven warming. Others aren’t convinced the “leprechaun” is entirely vanquished. “They are probably right in that [the AMO] is not as big a player globally as has sometimes been thought,” says Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado. ...If a grand ocean oscillation isn’t shaping climate, a future ocean cooling is unlikely to buy society time to address global warming. But the demise of the AMO also might make it easier to predict what is in store....