Back in my original cycle, I applied right out of undergrad for a couple of programs that I initially thought could fit my interests well. All of them ended up falling into two fields, Engineering or Earth/Climate Science, and I got into some good programs for earth science (e.g. Stanford and Berkeley). I ended up deciding to go to UPenn for Engineering since I thought I might enjoy the work there better but as I'm going through the motions, I feel like I'm not as into the specific research area my advisor is dealing with as I thought I'd be. I'm beginning to think I'd have enjoyed going into climate science instead a lot more, which is probably not the best conclusion to come to at this point...
My current department doesn't have a whole lot of faculty working in this specific area anyways - even the climate science department doesn't seem like it has a ton of projects I'd be interested in. I'm thinking of Master-ing out and potentially reapplying to some climate science programs instead. I haven't consulted my advisor on this yet. Additionally, I'm keeping up on my current research project/classes, and I intend to continue to do so until I officially leave, so it's not like I'm underperforming/slacking.
I'm wondering how exactly one would fare in this whole reapplication process. I presume my undergrad application was strong enough that I got into a couple of good programs so I would think a Master's plus additional research would surely add to that. I am worried on two accounts, however:
How exactly would my current advisor take the news that I'd like to explore a different field altogether? Let's assume I continue to do well, make good progress in terms of research, and get good grades, blah blah: would they be pissed? Should they be pissed? How should I break the news to them while ensuring the letter isn't tainted by some sort of vendetta?
How should I mention this on my application? And how should I approach the application process in general? A simple Google search tells me that most new programs I'd apply to would eye my application rather suspiciously if I do not have a "good reason" for leaving and that advisors might be wary of taking me on if I Master'd out since "what's stopping me from doing the same when I get to their program". Is it really that big of a hurdle? I'd like to think that changing interests, especially to a field that is not too far off from my current one, is a decent reason but I'd be curious to hear opinions.