Getting warmerHow can we know that increases in CO2 cause increases in temperature?
Get three big jars full of air, each containing a thermometer. Jar A is your control. Put it to one side. Add a small amount of CO2 to Jar B. Add 10x the amount of CO2 that you added to Jar B to Jar C.
Carefully irradiate all three jars, using the same amount of radiation and the same time.
One hour later, observe the temperature of the air in all three jars. End of discussion.
That really is it. We discovered the link in 1862. Nothing's changed.
But it might be a really small effect, right? Well, that seems feasible if you never experimented with different levels of CO2, or if small effects don't matter. The lab does not translate well to the atmosphere (the earth is not contained within a bell jar!), but the effect is big enough. And it doesn't have to be huge because it's incremental. Increasing the heat means more heat to radiate away when the sun isn't shining. And a small effect is enough. Think about our hot summers. A sheet is pretty thin but we have nights where sleeping with a sheet over you is unbearable. The analogy is quite close, because what causes the discomfort is that the sheet prevents you from radiating heat away. It only traps a little, but it's enough to make you feel uncomfortably warm.
Now imagine you have to keep yourself wrapped in the sheet, under your normal clothes, during the day.
On that subject, here is an excellent article on the "Climategate" scandal, which is a bit of a case study in how the media can beat up nothing much into something that looks big, fuelling the deniers, who don't require facts at the best of times.