When thinking of all the AGW pseudoscience swallowed by the GAC (Global Alarmist Church ... pronounced as G-A-C-K-K-K-K !!! with a gutteral ending as if you have a throat clogged with nasty phlegm and you are "hawking a loogie") you get an overwhelming involuntary reflex to spit on the nearest climatologist).
US southern slang. Usually preceded or followed by "now."
It means "listen to what I have to say next, because it is something that you were unware of or had previously been ignoring, much to our chagrin."
or can simply mean "look at this."