evidence: You’ve probably already read that carbon dioxide and other greenhouse gases act like a blanket or a cap, trapping some of the heat that Earth might have otherwise radiated out into space. That’s the simple answer. But how exactly do certain molecules trap heat? The answer there requires diving into physics and chemistry. [...] In the case of greenhouse gases, the planet’s temperature is a balance between how much energy comes in versus how much energy goes out. Ultimately, any increase in the amount of heat-trapping means that the Earth’s surface gets hotter. (For a more advanced discussion of the thermodynamics involved, check out this NASA page.) [...] As carbon dioxide and other greenhouse gases heat up the planet, more water evaporates into the atmosphere, which in turn raises the temperature further. However, a hypothetical villain would not be able to exacerbate climate change by trying to pump more water vapor into the atmosphere, says Smerdon. "It would all rain out because temperature determines how much moisture can actually be held by the atmosphere."