Some would call it more than just bromantic. I'm not sure how I feel about the deeper end.

So let me get this straight:
The way this magic (magery, I guess) works is that you need an element to use an element, as explained in the firewood analogy. As for the fire example you stated you can basically use the temperature of one's surroundings to fuel a flame. My question is, how much of your environment can you use? If someone was in, say, -50 weather in some ice cave, could they still conjure a large fireball or whatever through the temperature (and some good old Magi magic) and make all that ice even more frozen? 

Is there an actual limit to the resources you can use or are Magi supposed to use their own discretion?

Or am I getting this all wrong?