A common contrarian argument is that “water vapor is a more important greenhouse gas than CO2, but we don’t regulate evaporation”. For instance, Roger Helmer, a British member of the European Parliament put it this way.
But the Warmists have the bizarre idea that only CO2 matters. Certainly CO2 is a greenhouse gas, but it’s not even the most important one. That’s water vapour, and there’s nothing we can do about it (as long as the wind blows over the ocean).
You can read a good rebuttal about this over at Skeptical Science, so I won’t reinvent the wheel here. However, I made a nice infographic about why this “argument” is ridiculous… if you know any physics. Here it is, and use it however you like.