From Roy Spencer in the New York Post today :

Contrary to popular accounts, very few scientists in the world – possibly none – have a sufficiently thorough, “big picture” understanding of the climate system to be relied upon for a prediction of the magnitude of global warming. To the public, we all might seem like experts, but the vast majority of us work on only a small portion of the problem.
Here, for example, is an insight that even many climate scientists are unaware of: The one atmospheric process that has the greatest control on the Earth’s climate is the one we understand the least – precipitation.