[DaGman]

"...carbon dioxide, supposedly the culprit, makes up such a tiny fraction of the atmosphere that even if it were to quadruple, the effect on climate would be negligible;..."

Why does Ms. Phillips have to say this? CO₂ makes up 21% of the atmosphere, hardly "a tiny fraction".

[djf]

I believe CO2 is only about 3 percent.

[Egon]

Why does Ms. Phillips have to say this? CO2 makes up 21% of the atmosphere, hardly "a tiny fraction".

You're thinking of oxygen.

Introduction to the Atmosphere: Background Material

[DelaWhere]

Not even close to 21% - the atmosphere is composed as follows:

PERMANENT gases in the atmosphere by percent are:

Nitrogen 78.1%
Oxygen 20.9%

(Note that these two permanent gases together comprise 99% of the atmosphere)

Other permanent gases:

Argon 0.9%
Neon 0.002%
Helium 0.0005%
Krypton 0.0001%
Hydrogen 0.00005%

VARIABLE gases in the atmosphere and typical percentage values are:

Carbon Dioxide 0.035%
Methane 0.0002%
Ozone 0.000004%
Water Vapor varies

[Iris7]

You are thinking of oxygen, 21%.

[Doctor Stochastic]

You're thinking of O2 not CO2. CO2 is small, about .035%. CO2 is only important because it helps retain heat. http://www.met.fsu.edu/explores/atmcomp.html