If you look at various dictionaries, you will see that their research gives alternative pronunciations even for US usage. The dropping of the middle schwa by some US speakers is hardly extraordinary.

@edwin the middle "a" in caramel is not a schwa; it's a fully sounded vowel - there are three clear syllables in "caramel" in BrE and AusE, but only two, sans schwa, in NA.

AHD: caramel (kăr′ə-məl, -mĕl′, kär′məl) // Collins: (ˈkærəməl; -ˌmɛl) // RHK Webster's: (ˈkær ə məl, -ˌmɛl, ˈkɑr məl). Research you yourself should have done and presented.

@edwin good ref, but where I come from (Australia) we say "Carr-uh-mel"

And this is adequate to justify an unqualified 'But North Americans (Canadians too) don't pronounce the middle "a". They pronounce it exactly like the girl's name Carmel.'? ELU expects checked data, not opinion, to be stated assertively. The research Josh has found shows how misleading your assertion is.

@edwin OK. It's been my consistent experience. No ref. I'll amend my Q accordingly

I may perhaps have been to the States more often than you have, but I wouldn't have predicted anything like the pronunciation/usage distributions Vaux and Golder have found. And I wouldn't have considered it wise to guess. 'From my experience' needs qualifying to be admissible other than in a 'comment' on ELU. / A simple hedging 'many' would solve that problem, but you should have shown evidence of research here.

US Midwest: I've always said something close to "care-uh-mul". I mostly only hear "car-mel" when someone's speaking of the pudding. I certainly would believe, though, that some people hear "care-mul" when I say "care-uh-mul" -- what you hear tends to be conditioned by a sort of aural prejudice.

Why not ask why it's spelled as though it had 3 syllables when it clearly has only 2 syllables?

I say care-a-mull too, and I'm from the US

i say it this way: Caramel

Graham has a similar discrepancy I believe

I say care-uh-mell and I'm from USA.

And don't forget colonel.

I have often noticed that "diaper" and "diamond" are similar to "caramel"; American's say "diper" and "dimond".

@OldBunny2800 but in the USA "care" is pronounced "cehr"; you guys pronounce "a" as an "e" when it's followed by an "r", ie marry and merry are homophones in USA, which BTW doesn't sound (pun intended) right. So you really say "cehr-uh-mell", am I correct?

@MissMonicaE does my comment immediately before this one apply to you too?

"Squirrel" is similar

@Bohemian I'm not sure what sound you mean by "cehr." I say "caramel" with the same "care" as "I don't care." But I also say "merry" and "marry" differently, and in my mouth, "I want to marry him" is different from "marry" as a Shakespearean exclamation.

Don't get me started on "herbs".

@miss like the way USA pronounces scenario as scenerio, Mario as Merio, and marry as merry. It could be regional, but it's a pretty big region if it is, because all Americans (except the north east corner) do this vowel rotation

@Bohemian Then I guess yes. I know lots of Americans who say "cahr" in "caramel," though.

Do non-Americans say "mahrry"?

@EricLippert Wait, how do you pronounce diaper and diamond?

@miss non Americans say the "a" is marry exactly like "a" in "apple". Americans saying "mehrry" sounds as weird to us as I imagine pronouncing "apple" as "epple" would sound to Americans

@eric if "you" is me, we don't have the word "diaper" in our vocabulary (we use "nappy"), but would say it like what we hear Americans say, ie "di-per". And we say "di-mnd"

dictionary.cambridge.org/us/pronunciation/english/diaper Notice the subtle difference between American "di-per" and UK "di-a-per". The "a" is there but you have to listen for it.

Same with dictionary.cambridge.org/us/pronunciation/english/diamond though it is more noticeable with diamond.

@Bohemian I find that claim about Mario doubtful in my experience as a video game player. All of Super Mario's American actors, who are Lou Abano of the Super Mario Super Show; Bob Hoskins of the Super Mario Bros. Movie and Charles Martet of Super Mario Mario 64 seem to use an open a sound to me. Charles fakes an Itallian accent though, so that might not count as much.