October 25, 2006
Did the Rise of Mountains Cause the Lowering of Temperatures?
I'm a global warming skeptic - and by that I mean I'm skeptical that human actions are the driving factor behind current climate change. Now, that doesn't mean we aren't, that just means I'm not convinced that we are. So I read this article on a connection between the Appalachian Mountains and global cooling with interest -- not because it supports my skepticism, but because it doesn't.
One such debate is whether atmospheric carbon dioxide truly drives Earth's climate. The planet has shifted between greenhouse conditions and icehouse conditions throughout its history, and research from Saltzman's team strongly suggests that carbon dioxide levels are a key cause."In this study, we're seeing remarkable evidence that suggests atmospheric CO2 levels were in fact dropping at the same time that the planet was getting colder. So this significantly reinforces the idea that CO2 is a major driver of climate," Saltzman said.
...
"We observed a major shift in the geochemical record, which tells us something must have changed in the oceans," Young said.
The timing of the strontium ratio decline matches the rise of the Appalachian Mountains . The crustal plate underneath what is now the Atlantic Ocean pushed against the eastern side of North America, lifting ancient volcanic rock up from the seafloor and onto the continent.
This kind of silicate rock weathers quickly, Young explained. It reacts with CO2 and water, and the rock disintegrates. Carbon from the CO2 is trapped in the resulting sediment.
The chemical reaction that weathered away part of the Appalachians would have consumed large amounts of CO2 from the atmosphere –- right around the time that the Ordovician ice age began.
When I read the first part, I immediately thought to myself does it tell us that CO2 drives temperature, or temperature drives CO2. And that's always the hard question - which change came first - CO2 or temperature. But part 2 contains an explanation that we would expect the CO2 to drop for a reason other than temperature, which surely strenghthens the case for CO2 to drive temperature, and not the other way around.
So we have one case, and the article goes on to say that the rise of the Himalayas may have caused our current ice age (we're in an interglacial period at the moment). So now we have two possibles, and wikipedia claims there have been 4 major ice ages.
That leaves us with some unanswered questions, like what about the other two ice ages, and how did CO2 get back into the atomosphere to end an ice age, and what is driving our current cycle of glacials/interglacials? I'm still stuck with suggestive, but not conclusive.
Posted by Kevin Murphy at October 25, 2006 12:28 PM | Science
