evidence: Over time, scientists began to develop a more nuanced view of how gases form and act. Not all gases on Earth are greenhouse gases. The amount of greenhouse gases in the atmosphere depends on sources (natural and man-made processes that produce them) and sinks (reactions that remove the gases from the atmosphere). Carbon dioxide is only part of that equation, and only the second most abundant greenhouse gas on Earth. [...] It’s tempting to think that because CO2 has so many counterparts, it’s not worth worrying about. But just because CO2 isn’t the only greenhouse gas doesn't mean it’s not cause for concern. "A lot of people use [greenhouse gases] to downplay the importance of carbon dioxide," says Davis. "That’s the biggest issue we face." Some gases may be more abundant, but none stand alone—and with CO2 rates rising at unprecedented levels, it’s difficult to estimate just how dire the consequences of unchecked emissions of any kind might be.