"Unless we know how the greenhouse-limiting properties of precipitation systems change with warming, we don't know how much of our current warmth is due to mankind, and we can't estimate how much future warming there will be, either. To solve the global-warming puzzle, we first need to learn much more about the precipitation-system puzzle.What little evidence we now have suggests that precipitation systems act as a natural thermostat to reduce warming."
Roy W. Spencer
Principal research scientist at the Global Hydrology and Climate Center of the National Space Science and Technology Center.
As quoted here, in this article about climate models.
"The practical experience of numerical modeling in allied fields such as semiconductor process modeling should cause us to question the claimed accuracy for Global Climate Models. The UN's distortion of historical climate data should further undermine our faith in climate models because such models can only be 'tested' against accurate historical data."