Do we not already have so much CO2 emissions that its effect on infrared radiation is “saturated”?
Some people have argued that simple physics shows that there is already so much CO2 in the air that its effect on infrared radiation is “saturated” – which means that adding more gas can make little difference to how much radiation passes through the atmosphere because all the radiation is already blocked.
The simple physics explanations for the greenhouse effect that you find on the internet are often quite wrong. These well-meaning errors can promote confusion about whether humanity is truly causing global warming by adding carbon dioxide to the atmosphere. Some people have been arguing that simple physics shows there is already so much CO2 in the air that its effect on infrared radiation is “saturated”— meaning that adding more gas can make scarcely any difference in how much radiation gets through the atmosphere, since all the radiation is already blocked. And besides, isn’t water vapor already blocking all the infrared rays that CO2 ever would?
Here is how to answer on the “saturation argument” against global warming:
(a) You’d still get an increase in greenhouse warming even if the atmosphere were saturated, because it’s the absorption in the thin upper atmosphere (which is unsaturated) that counts
(b) It’s not even true that the atmosphere is actually saturated with respect to absorption by CO2,
(c) Water vapor doesn’t overwhelm the effects of CO2 because there’s little water vapor in the high, cold regions from which infrared escapes, and at the low pressures there water vapor absorption is like a leaky sieve, which would let a lot more radiation through were it not for CO2, and
(d) These issues were satisfactorily addressed by physicists 50 years ago, and the necessary physics is included in all climate models.
e) Doubling CO2 from pre-industrial levels will lead to an increased “radiative forcing” of around 3.7 W/m2, and this part of climate science at least, is well understood.