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.