Monday, May 14, 2007

Nothing personal, Milankovitch

One thing that my paleoceanography teacher harped on A LOT this last semester was Milankovitch theory. Milankovitch, Milankovitch, Milankovitch. We talked about it so much I kinda hate Milankovitch, which is dumb because he died almost 50 years ago. I’m sure he was a good enough guy, it’s just that that class made me cranky.

Milankovitch was a Serbian engineer and mathematician who put together a theory about why the Earth goes thru cycles of glacials and interglacials. You see, nobody knows why the Earth has these long, cold periods called glacials. Finding out why the Earth goes thru these hot and cold periods is a big deal to researchers right now since we’re faced with the looming possibility of total climate annihilation!

To better predict the future, climatologists are looking at the past. The last glacial ended less than 20,000 years ago, which isn’t very long in geologic time. During glacial times is when we had awesome beasts like mastodons and saber tooth tigers, but unfortunately it provided the premise for the movie “Ice Age” and therefore contributed to the salary of John Leguizamo.

Milankovitch proposed that we get cycles of glacials and interglacials because of the Earth’s orbit with respect to the sun. We have 3 flavors of variation:

1.) Eccentricity – has to do with how elliptical the earths orbit is. Sometimes the Earth’s orbit around the sun is more circular than at other times. Further from the sun = less solar energy = colder. Eccentricity varies on a 100,000 year time scale.


2.) Obliquity – the Earth is tilted a little bit on its axis. Sometimes the Earth sits more up and down, but sometimes it’s more slanted. Obliquity varies on a 40,000 year time scale.

3.) Precession – imagine a top spinning around. Or a dradle (ooooo! I went there) You get a little bit of wobble as it spins around. The Earth does that too and the wobbling is called precession. This process affects the Earth’s orbit on a time scale of about 20,000 years.


Problem is that none of these mechanisms fit perfectly with the records of past glacial and interglacial cycles. It’s not like every 40,000 years and BOOM! The Earth gets super cold. Glacials happen because of a combination of factors, a combination that will make someone rich when they figure it out. But Milankovitch theory has not been totally poo-pooed yet, it’s still got its valid points. So props to Milankovitch, even though I’m totally sick to death of hearing about him.

1 comment:

Mark said...

Awesome post, yet again!

I just found out about this blog, but I'm a fan already!

(Oh, and there was a typo: for the move “Ice Age”)