“The sun warms the Earth’s surface, which causes the Earth’s surface to emit longwave radiation.
Greenhouse gases like H2O and CO2 absorb certain wavelengths of longwave radiation emitted from the Earth’s surface. This adds energy to those molecules, which gets transferred to nearby molecules as heat. Without the greenhouse gas molecules, that energy would have been directly transmitted back into space without warming the atmosphere.”
Tony is right in this quote. But the scale of such effects needs to be put into perspective relative to another effect of the infra-red active gases. The solar insolation at the top of the atmosphere was 1365.8 W/m2 in 2010. So on a cloudless day and with no infra-red active (so-called greenhouse) gases or gases that absorb ultra-violet light, there is a time when this 1365.8 W/m2 would be incident upon the Earth’s surface. Let us examine the top of the atmosphere solar radiation spectrum and compare it with the solar radiation spectrum at the surface.