Definitely say something. I'd say speak to the teacher first - even an email would do, as long as you received a courteous and timely reply.
If you didn't receive a satisfactory reply from the teacher, I'd send an email to the head teacher, ccing the teacher into it.
If I had guts, I say something along the lines of:
'I can see where you're coming from, America doesn't have the best track record - but the comments, whilst (hopefully) said to encourage students to take pride in intellectualism were, in themselves, quite small-minded. I know its easy to take a stab at America here and there, and trust me, I understand, I'm the one who emigrated from it! - but I wonder if having an American pupil in your class makes comments and views like 'rich Americans who don't believe in climate change' go from 'not a big deal' and pretty mainstream to being framed it in the context of what they really are, ie judging whole swathes of people, inaccurately, in a somewhat bigoted fashion (ie there are many MANY wealthy Americans who believe in climate change).'
Best of luck to you and keep us updated!
-Eliza (mother, american, brit resident 7+ years, secondary school history teacher trained in the UK)