The coldness comes from space, which is very very cold. We tend to lose most of our heat to space via radiation, rather than convection. The difference is betwe

The coldness comes from space, which is very very cold. We tend to lose most of our heat to space via radiation, rather than convection. The difference is between one of those infrared dish heaters, and a heater that blows warm air. CO2, being rather opaque in the infrared, doesn't let the heat escape into space. Instead, the radiation is reflected back into the atmosphere, heating the planet and the oceans