> How do we know that right now it's because of CO2 and not because of some process by the planet? The short answer is "because there's an entire field of scie

> How do we know that right now it's because of CO2 and not because of some process by the planet? The short answer is "because there's an entire field of science that models this and figures out what contributes to global climate". Things we know contribute to the global temperature include: the atmospheric composition, the albedo of the surface, and the change in the axial tilt. The latter is currently what we understand to be the main driver of the glacial periods [we are still in the Quaternary Ice Age; we are currently in an inter-glacial period, when the glaciers have retreated toward the poles]. Greenhouse warming was also predicted well before it occurred, if it makes you feel any better; back in the 19th century people said, "Hey, we just found out that CO2 makes greenhouses warmer, and we're burning enough coal to have a measurable effect on the composition of the atmosphere; if this keeps up we should expect the Earth to begin warming up." And then, over the next century, we did and it did. > I've heard people say that both warmer weather and colder weather are both evidence that the climate-change theory is right. Warmer and colder weather in various places is expected, but the mean global temperature just keeps going up, up, up. It's not like we're having "coldest years on record" and then going, "Yeah, climate change is confirmed again". We have the hottest year on record, year after year, and then the polar vortex goes all wibbly-wobbly and blasts somewhere with weeks of cold. But the overall global temperature is still pretty damn warm.