If a scientist is evaluating subjects (often well) outside their sphere of study, how does that make their opinion any better than anyone elses?

"And while 84% of scientists say the Earth is getting warmer because of human activity, less than half of the public agrees with that."

So "all" the non-climate related scientists evaluated the GW claims and read the papers and make their own opinions?

OR

Do they rather simply believe what they're taught in school?