<?php echo date("Y"); ?>
On a side note, when formatting dates in PHP it matters when you want to format your date in a different locale than your default. If so, you have to use setlocale and strftime. According to the php manual on date:
To format dates in other languages, you should use the setlocale() and strftime() functions instead of date().
From this point of view, I think it would be best to use strftime as much as possible, if you even have a remote possibility of having to localize your application. If that’s not an issue, pick the one you like best.