In his book/film An Inconvenient Truth, Gore relates a conversation he had with Carl Sagan, noted astronomer and host of a popular PBS series on science, where Sagan said:  “If you had a globe covered with a coat of varnish, the thickness of that varnish would be about the same as the thickness of the Earth’s atmosphere compared to the earth itself.”

Sounds pretty fragile, doesn’t it? Al  thinks so:  “The most vulnerable part of the earth’s ecosystem is the atmosphere.  It’s vulnerable because it’s so thin.”

Two problems with this:

First of all, like most analogies, it sounds good, but doesn’t quite work.  Do the math.  (Al can’t.  He got a D in astronomy at Harvard.)  So how big exactly is the atmosphere?  In a break with tradition in the climate science area, we’ll show you our data.

The consensus number from various websites  is:

The diameter of the exosphere is 10,000 + 10,000 + 12720 (diameter of the earth) = 32720km. The radius is therefore 16360km.

The volume is four thirds multiplied by pi multiplied by the radius cubed (4/3 π 16360³) = 18,341,650,640,000 km³

Less the volume of Earth occupied by Earth. (4/3 π 6360³) = 1,077,605,665,000km³

18,341,650,640,000 – 1,077,605,665,000 = 17,264,044,985,000km³

Yow. 17.2 trillion cubic kilometers. But there’s a better measure: mass. And that number is 5 × 10(18) kg, another whopping number.  Still another number is the “effective volume,” which reduces the boundary between atmosphere and space from 100 km to 10 km, as most of the actual mass (90%) of the atmosphere lies below 10 km.  That number?  4.2 billion cubic km.

(Thanks to reader Tom G for catching an earlier error in this calculation — see comments below.)

Second problem:  the total volume of the earth’s oceans is about 500 million cubic kilometers.  That’s about 11% of the atmosphere’s size.  So the atmosphere is over nine times as big as the world’s oceans.  Wouldn’t that make the oceans the “most vulnerable part of the earth’s ecosystem?”

Now, this is not to say that we can’t — and haven’t — screwed the atmosphere up royally by fouling it with everything from burning tires to underarm deodorant spray, but no one here is saying we should pump anything we like in any quantity we like into the air we breathe.  But please don’t try to scare us into buying your personal profit agenda (yes, Al, that’s you I’m talking to, the guy with a bigger carbon footprint than Ecuador) with dumbed-down imagery that anyone– even a D student — can punch a hole in with a pocket calculator.

Now, about those oceans….