Carbon Dioxide Doesn't Absorb Solar Radiation, But Water Vapor Does
At the heart of the greenhouse theory of climate change is that greenhouse gases like carbon dioxide absorb solar radiation while preventing heat from escaping, similar to how a greenhouse traps warm air but allows in sunlight.
Carbon dioxide certainly does prevent heat from escaping into space; it’s essential to preserving the atmosphere. Carbon dioxide is heavier than other elements in the upper atmosphere like hydrogen and helium, preventing it and other surrounding gases from drifting off through atmospheric escape. Without carbon dioxide, the planet would lose its atmosphere to space and be much colder like the moon.
While carbon dioxide helps form that barrier between the atmosphere and space, it doesn’t absorb solar radiation in any meaningful way.
Based on data from HITRAN via SpectraPlot, carbon dioxide’s maximum absorption value is 1/2,559th that of water vapor. Carbon dioxide also only absorbs solar radiation in a limited spectrum—about 5 percent of the range of frequencies that water vapor does.
While certain greenhouse gases like methane and nitrous oxide do have significantly higher absorption rates than water vapor and carbon dioxide, they are not in any way abundant in the atmosphere and only absorb solar energy across a very limited spectrum.
According to the National Oceanic and Atmospheric Administration (NOAA), carbon dioxide makes up 0.035 percent of the atmosphere while methane is 1.70 parts per million. That is, there is 20,588 times more carbon dioxide than methane.
Other greenhouse gases with substantial absorption rates are even more rare. Carbon dioxide is 500,000 times more common than ozone and 112,903 times more common than nitrous oxide.
Water Vapor is a Greenhouse Gas
Technically, water vapor in the atmosphere—otherwise known as humidity—is also a greenhouse gas as it does absorb a significant amount of solar radiation and is abundant in the atmosphere. Yet water vapor is not considered a concern for climate change for reasons unknown.
Prevalence of water vapor is heavily dependent on location—e.g. swamps versus deserts—so it can be anywhere from zero to four percent of the atmosphere. Yet even at the global average of .4 percent, that would be 10 times more prevalent than carbon dioxide.