the red glow not what you think

agreed

Its obviously Godzilla's lava lamp. Case closed. 

lol

I think its his night light.

I.... Didn't even realize there was a theory behind it.... I just assumed it was from a fire somewhere....

I disagree, we don't know what colour godzilla's atomic breath is. After all it's a reboot. Anyway I think that's probably the intense heat godzilla's giving off.

Pretty sure godzilla's nuclear breath is blue in this movie. Fire doesn't shine a bright red. Probably flares

It's probably a flare. Plus if Godzilla had his Sprial Atomic Breath (which he most likely won't in this film) the shot is to lower to see him charge it. His tail doesn't flicker or glow when he charges his Atomic Breath, just his sails.

Like a sunrise, you can see the shine before the actual thing. Thats what we see in that picture, something is shining bright behind him

i think it could be his nuclear breath.  He has had red fire in the 90's and 2000's eras.

Godzilla farted over a fire and POOF! there you have it....

AGGRESSIVEKAIJU45 - We actually DO know what color his atomic breath will be. It's been confirmed by more than one source, including the toys, that it's going to be blue.

The only two reasons behind that glow are either fire, or a flare, as stated by KAIJUFALL3 in the main post.