The Richard Feynman quote seems appropriate here.
Compare it directly with observation to see if it works. If it disagrees with experiment, it's wrong. In that simple statement is the key to science. It doesn't make a difference how beautiful your guess is, it doesn't make a difference how smart you are, who made the guess or what his name is. If it disagrees with experiment, it's wrong. -- Video
Physicist Howard Hayden's one-letter disproof of global warming claims [pre-Climategate]Dear Administrator Jackson:
I write in regard to the Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act, Proposed Rule, 74 Fed. Reg. 18,886 (Apr. 24, 2009), the so-called "Endangerment Finding."
It has been often said that the "science is settled" on the issue of CO2 and climate. Let me put this claim to rest with a simple one-letter proof that it is false.
The letter is s, the one that changes model into models. If the science were settled, there would be precisely one model, and it would be in agreement with measurements.
Alternatively, one may ask which one of the twenty-some models settled the science so that all the rest could be discarded along with the research funds that have kept those models alive.
We can take this further. Not a single climate model predicted the current cooling phase. If the science were settled, the model (singular) would have predicted it.
(excerpted from Professor Hayden's letter to Lisa P. Jackson, Administrator Environmental Protection Agency. More at link.)