When a discussion of “greenhouse gases” takes place, one sometimes wonders if the reader is aware of the make up of the Earth’s atmosphere. Many of you, especially the engineers and scientists that read this blog, know about the elements that make up the atmosphere and what the carbon cycle is. But for those that don’t have this background, this may help.
The measured atmospheric CO2 is about 400 parts per million (ppm) at present. That means that for every 1,000,000 gas molecules in our atmosphere, about 400 of the gas molecules are carbon dioxide.
Lets look at several charts prepared by University Corporation for Atmospheric Research (UCAR) to give the reader a feel for the composition of the elements in dry air. UCAR explains diagrams 1 and 2:
“The following two diagrams may help you visualize how much 400 parts per million is. Each rectangle is 600 by 400 pixels in size, and therefore contains just a bit fewer than a quarter of a million pixels (240,000 = 600 x 400). At this scale, carbon dioxide represents slightly less than 100 pixels (actually 96 pixels = 400 parts per million times 0.24 million). The first diagram shows 96 black dots (representing carbon dioxide molecules) scattered throughout the rectangle (which represents the whole atmosphere).”
Diagram 1: CO2 at 400 ppm in dry air. The block contains about 250,000 blue pixels and about 100 black pixels, the latter representing CO2 molecules.
How does 400ppm CO2 compare to other gases in Earth’s atmosphere? The following UCAR diagram provides the following visualization.
- nitrogen (N2) 78%–the blue
- oxygen (O2) 21%—the red
- argon (Ar) almost 1%—the green
- carbon dioxide (CO2) 0.04%–the black
- (everything else (neon, helium, methane, krypton, hydrogen,…) less than 28 ppmv)
Based on what the media tells you, these charts may surprise you by the very small amount of CO2 in the atmosphere.
There is something else you need to know. The preceding set of numbers are calculated in “dry air”. In fact, there usually is water vapor in the Earth’s atmosphere. Generally speaking it is in the range of 1 to 4% (100 times CO2). Water vapor is a greenhouse gas. It is a much more significant greenhouse gas than CO2. It has been estimated that water vapor represents up to 90% of the “greenhouse gas” effect.
This the beginning of a several part look at CO2 and its role in global warming.
Coming in the next posting. CO2 Causes What? Part 2 The Carbon Cycle