I read through that link a bit and calling them all "scientists" is... uhh... disingenuous.  Apparently all you need is a "formal educational degrees at the level of Bachelor of Science or higher in appropriate scientific fields." 
2.6k signers are mechanical engineers.  I'm a mechanical engineer and I certainly don't feel qualified to sign the petition.  500 aerospace engineers.  7.2k general engineering degrees.  2.1k electrical engineers.  400 metalurgists!?  Huh?  Entomology?  Animal science?  Medicine?  I believe some people who signed the petition reviewed the available data and are qualified, but there's no way I believe all 31k of them are.