One of our most-read old posts is the step-by-step explanation for why increasing CO2 is a significant problem (The CO2 problem in 6 easy steps). However, that was written in 2007 – 15 years ago! While the basic steps and concepts have not changed, there’s 15 years of more data, updates in some of the details and concepts, and (it turns out) better graphics to accompany the text. And so, here is a mildly updated and referenced version that should be a little more useful.
Step 1: There is a natural greenhouse effect.
https://upload.wikimedia.org/wikipedia/commons/thumb/b/bb/The-NASA-Earth%27s-Energy-Budget-Poster-Radiant-Energy-System-satellite-infrared-radiation-fluxes.jpg/776px-The-NASA-Earth%27s-Energy-Budget-Poster-Radiant-Energy-System-satellite-infrared-radiation-fluxes.jpg
The fact that there is a natural greenhouse effect (that the atmosphere restricts the passage of infra-red (IR) radiation from the Earth’s surface to space) is easily deducible from; i) the mean temperature of the surface (around 15ºC) and, ii) knowing that the planet is normally close to radiative equilibrium. This means that there is an upward surface flux of IR around \sigma T^4 (~398 W/m2), while the outward flux at the top of the atmosphere (TOA) is roughly equivalent to the net solar radiation
— source realclimate.org | Gavin | 10 Jul 2022