The most famous meteorite collision in history, or prehistory, is the one widely believed to have taken out the dinosaurs. (Widely but not universally; there is a tragicomically and astoundingly bitter scientific dispute over an alternative hypothesis.) But there’s increasing speculation that a sudden mysterious cooling just as the last glaciation was ending, known oddly as the “Younger Dryas”, might have been due to the planet taking one on the chin, or rather the Hiawatha glacier in northwestern Greenland, about 12,800 years ago. My goodness but climate is complicated. Except in the late 20th century when it’s all CO2, right?
If correct, this meteorite theory supplants the notion that it was the bursting of a great ice dam that let vast quantities of glacial meltwater pass down what would become the St. Lawrence and in doing so upset the Atlantic meridional overturning circulation, a massive current taking warm water north from the Equator. But whatever it was, it caused temperatures to plummet “in Greenland by 4 to 10 °C (7.2 to 18 °F)” in a remarkably short period, just decades.
Obviously if you think CO2 determines temperature the whole ice age is a mystery. No, sorry, we mean you need ad hoc explanations for every sudden change that clearly isn’t related to CO2 which is all of them. And yes, if you were wondering, there was an Older Dryas and even an Oldest Dryas that don’t have a plausible CO2 explanation. They don’t get much press partly because their existence is unclear. But the Older seems to have happened around 12,000 BC, give or take 400 years, and lasted about two centuries, and the Oldest is tentatively placed “about 1,770 years earlier” and lasted maybe 400 years.
These periods also create problems for the new theory. Possibly there was a run on meteorites just at that time. But if not, what made these other Dryases happen? (If you are wondering, which we were, Science magazine explains that the name comes from “a small white and yellow arctic flower that flourished during the cold snap”. And while we’re fussing about terminology, meteoroids fly through space, meteors burn up in the atmosphere and meteorites hit the ground, sometimes gently and sometimes not.)
Well, some people emerged from a cave to blame volcanoes. No, really. And one of the researchers mucking about in Hall’s Cave in the Texas Hill Country said bluntly “This work shows that the geochemical signature associated with the cooling event is not unique but occurred four times between 9,000 and 15,000 years ago. Thus, the trigger for this cooling event didn’t come from space. Prior geochemical evidence for a large meteor exploding in the atmosphere instead reflects a period of major volcanic eruptions.”
Another study says that volcanic eruptions might have caused a decline in Israeli wine production. Which if you’ve had kosher wine might lead to three cheers for volcanoes. But the study refers to a sudden cooling during a cooling, a particularly dismal period around 540 AD during the cooler Dark Ages between the Roman and Medieval Warm Periods that led to the abandonment of formerly high-quality vineyards in what is now the Negev Desert so maybe it wasn’t horribly sweet back then. (OK, to be fair, Israeli wine is a lot better now than it was 40 years ago.) It also seems to have contributed to the spread of the horrifying Plague of Justinian due to crop failure and weaker immune responses when people were hungry, so don’t go thinking only warming is bad. Or that we know all about climate change and its causes.
Climate science, one might be led to speculate, is not entirely settled. Nor is the climate itself. As Wikipedia says, “The Younger Dryas was a period of climatic change, but the effects were complex and variable. In the Southern Hemisphere and some areas of the Northern Hemisphere, such as southeastern North America, a slight warming occurred.” Climate is complex and variable? Why weren’t we told?
Actually there’s a very real possibility that the Earth’s climate is so complex and variable as to be “non-linear,” that is, so complicated that genuinely minor initial “butterfly effect” causes reliably have major disruptive effects. Phys.org reported re the Texas cave study that “The Earth’s climate may have been at a tipping point at the Younger Dryas, possibly from the ice sheet discharge into the North Atlantic Ocean, enhanced snow cover and powerful volcanic eruptions that may have in combination led to intense Northern Hemisphere cooling”. But what if the Earth’s climate is frequently at “tipping points” because it’s just inherently an unstable kind of a thing?
It would explain a lot, for instance the demonstrated instability of the Earth’s climate over long and short time spans. But if so, it’s fatuous to pick one change you fancy, say the late 20th-century warming, and insist that it and it alone had a different simple linear cause, one that was previously insignificant or absent but suddenly and forever onward dominant.
The “scientific” dispute over the cause of the dinosaur extinction described in the Atlantic article sounds a bit like that over anthropogenic climate change! OMG can it be that scientists are just human beings and subject to all the pressures and bad behaviour the rest of us suffer from? No, impossible. “the science is settled“ everyone knows that!