Another way of looking at it is that in four of the words you can form a word using the first few letters: Car, Real, Bus, and Blank. However, you cannot do this with "Climate".
Another answer is that "Realise" is the only word that doesn't begin with the second and third letter of the alphabet...There's almost no end to the different interpretations.
Thanks for all your help. No, there wasn't a theme which makes it quite tricky to work out the answer they're looking for! Might submit a couple of the above suggestions.
Posting an update as I've just seen the solution in the magazine. Absolutely impossible in my opinion to have guessed this! Blanket - the others begin with the first three letters of successive American presidents: Carter, Reagan, Bush, Clinton. The next word should, therefore, also start with BUS for Bush (George W) and not the first three letters of our former prime minister: BLAir. It's also the word with the fewest vowels.