Yep, this is an RTFC situation.I just picked up a fun rules snippet from an article...the damage generated by Burning Earth can be redirected to planeswalkers. So not only can you tie down UXx decks manawise, you can kill their Jace with their own spells. Too funny...
Whenever a player taps a nonbasic land for mana, Burning Earth deals 1 damage to that player.
If it had been a source you don't control doing that damage, or had it been loss of life, or simply a trigger that stated no source, you wouldn't be able to redirect, but since Burning Earth is the source and you control said source, you can indeed
choose where the damage goes.