why do only certain gases cause the greenhouse effect and why do some gases have more of an effect than others eg. Methane is “worse” than CO2?
In: Chemistry
The shape of certain molecules means that the radiation from the sun is absorbed into the molecule.
Eventually the gases form a layer that because it impedes the rays ability to go through, it is then reflected.
the reason that some are worse is that some molecules absorb more radiation the more of methane in the atmosphere, the more likely that radiation is blocked or reflected compared to carbon dioxide, which absorbs less so more methane is worse than more carbon dioxide
Other molecules can also react differently when exposed to the radiation from the sun.
For example CFCs, which where banned for damaging the ozone layer, causes a reaction with ozone (o3) when exposed to UV rays. A chain reaction occurs where a single CFC molecule can react with 3 or 4 ozone molecules. Ozone is important since it reflects UV rays, UV rays still transfer energy and can contribute to global warming. Although CFC is not a greenhouse gas, it still contributes to global warming.
There are a variety of factors, the first of which is persistence, basically how long on average will the gas stay in that part of the atmosphere doing damage, the longer it stays up there, the more damage it does so it is a measurable amount worse than another gas. Other gases impact the other gas in our atmosphere having a direct impact on the components of the atmosphere so for instance can convert carbon monoxide into carbon dioxide. But the key measure is the extent to which the gas absorbs infrared radiation.
Greenhouse gas molecules vibrate in particular patterns, which allows them to absorb infrared light only at specific wavelengths. As you add more of a gas, its ability to absorb additional light becomes less, because most of the light it responds to has already been absorbed. The extra absorption never goes to zero, but it’s a a “diminishing returns” thing: the first gigaton of a gas you add to the atmosphere causes a lot more warming than the 100th.
Earth’s atmosphere already has a fair bit of CO2 in it, so its specific wavelengths of infrared light are already mostly (but not totally) blocked. The atmosphere has very little methane, so those particular wavelengths are almost wide open: a little bit of methane will do a lot to “seal up the hole” in this part of the greenhouse.
If the Earth’s atmosphere were rich in methane and poor in CO2, the effect would be reversed.
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