“There is no question that climate change is happening; the only arguable point is what part humans are playing in it.” –David Attenborough
If the Earth didn't have any global warming at all, our planet's mean temperature would be 255 K, or about -1º Fahrenheit: the mean temperature of the Antarctic continent. As it stands instead, our planet is much warmer than that, owing to the warming, insulating effects of the atmosphere, which is largely transparent to (incoming) visible light, but traps a fair amount of the (outgoing) infrared radiation.
This effect is even more spectacular on our inner, sister planet, Venus. While Venus might be more reflective and twice as far from the Sun as Mercury, its greenhouse gases and insulating cloud layers are so effective that it's actually the hottest planet in the Solar System, outstripping Mercury day or night.