"Understanding the role of clouds in regulating both weather and climate is at an early stage, and remains a critical unknown factor in predicting the extent of global warming."
Bigdavediode has it wrong again. Water Vapor has a dual effect. It is a greenhouse gas and has a much greater impact than CO2. It also forms clouds which reflect a large amount of the Suns energy from the Earth. Piel's analysis is accurate.
Save us from what? The Earth has been hotter than it is today. The Earth has had considerably higher concentrations of CO2 in the atmosphere than now. What exactly do we need to be saved from?
Thank you for correcting me that water vapor is a greenhouse gas when I posted that water vapor is a greenhouse gas and contributes to the feedback mechanism of man-made CO2. I'm not sure how "I had it wrong again" but I'm sure you'll point it out somewhere. The difference between CO2 and water vapor is that water vapor in high concentrations is known to fall out of the sky in the form of rain.
Flooding and storms, for starters. The Earth that you're referring to, did it have any problems with flooding?