Not uncommon. It's sometimes used to imply credibility to the text. And sometimes the footnotes are just made up. Look at Manual Puig’s Kiss of the Spider Woman or Vladimir Nabokov’s novel, Pale Fire or The Athenian Murders, by José Carlos Somoza. Often they are used comically like in The Bartimaeus Trilogy by Jonathan Stroud
You might be interested in this review (by a doctor of meteorology) of Cricton's novel. Here's a sample:
"On a scientific level, Crichton has obviously done a lot of research. The high-tech schemes of the baddies to create fake climate mayhem are all delightfully improbable, but based in fact just enough to leave you wondering if such things are really possible (not!). Unfortunately, Crichton presents a error-filled and distorted version of the Global Warming science, favoring views of the handful of contrarians that attack the consensus science of the
IPCC."
(broken link removed to http://www.wunderground.com/resources/education/stateoffear.asp?MR=1)