“But Trace Gas”

CO2 is a tiny part of the atmosphere. Yet it can haz big effects.


[LUIS] CO2 concentration in Earth’s atmosphere to the nearest hundredth of one percent: 1990: 0.04% […] 2020: 0.04%

[EVAN] So even if Australia somehow completely de-industrialised today and our contribution to global carbon emissions went from 1.3% to 0% a whopping 99.99998% of the atmosphere would be unaffected.

Objections and Replies

(Very Smol) 0.04% is small. –

Reply. Here is what 0.04% looks like (Kevin Pluck).

(Smol) 2 W/m² is a small amount.

Reply. It only takes .7 W/m² to in or out of a glacial period. The .2 W/m² adds .12K/decade, and that doesn’t cover the energy passed to other air molecules (Dan).

(No explanation) That does not explain anything. –

Reply. Each part of the Earth’s surface emits heat in the form of infrared (IR) radiation. The peak of this emission is right at the frequency where CO2 absorbs strongly. While the proportion of CO2 in the atmosphere is small, 380 parts per million or 0.038%, this is still a large number of molecules, large enough that near the surface, at wavelengths where CO2 absorbs, the average distance light will travel before being captured is a few meters (a couple of yards). See Eli’s Simplest Explanation for more details.


{Pedagogical} This talking point is a bit silly, but pedagogical. To visualize the effects of carbon dioxide is crucial to make people realize how AGW works.

{Incredibilism} Rejecting the influence of CO2 on atmosphere is the purest form of climate denial, but sometimes the point only expresses incredulity.