Yesterday at a pre-semester staff meeting, a manager stressed the importance of incoming first-year students becoming ‘acclimated’ to university life. I have never consciously encountered that word (I would unhesitatingly use ‘acclimatised’ – in fact in this context I would say something like ‘settle in’), and judging from the murmur around me, neither had some of my colleagues. I was possibly the only one who investigated further when I got home.
Google returns 856,000 results for acclimate and its default dictionary marks it as ‘North American’ (the manager is indeed North American). This compares with 495,000 results for acclimatize’ and 415,000 for acclimatise. Acclimate is the earlier form, dating from the late 18th century, compared with the mid-19th century for acclimatize/ise.
Google Ngram Viewer shows a big increase in acclimate from the 1960s, overtaking acclimatize in 1980s. Acclimatize and acclimatise together add to just short of acclimate. Intriguingly, acclimatize and acclimatise are also increasing in use, although less quickly that acclimate.
The ngram for American English is broadly similar to the overall one, but the one for British English shows acclimatize, acclimatise and acclimate in that order. Yes, despite -ise being ‘British spelling’, acclimatize has been used more often since the 1920s.
The only other instances of ac+noun > verb I could reasonably find are accompany and acknowledge. Otherwise, noun + ize/ise > verb is a far more common derivation.
There’s no great bother here. I understood a varietal word in context, and from what I’ve found online, the two words seem to co-exist. My choice is still acclimatise, but I am unlikely ever to use it.
(BTW, Word for Mac and WordPress both accept acclimate and acclimatize, but red-underline acclimatise.)
Never Pure and Rarely Simple 
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