People with just any old Bachelor of Science degree could add their name, too, as that was the sole qualifier.
Dentists, veterinarians, anyone with 4 years of college that resulted in a BS.
That is according to their own written criteria, by the way: http://www.petitionproject.org/gwdatabase/GWPP/Qualifications_Of_Signers.html
From their own web site: "Most of the MD and DVM signers also have underlying degrees in basic science".
Yippee, I guess.
Having 31,000 people sign something is not science. It is laughable.
Having 31,000 people sign something, when many are demonstrably unqualified to intelligently render an answer on the subject, is pitiful and does not help your cause.
The signers of the UN climate change “consensus” have a similar array of “professional scientist” qualifications. Precious few of them even reviewed the key portions of the UN report.