I noticed the same with my ads across all of my properties. Google is most likely testing different justifications, as I've seen other variations like horizontal & vertical text alignment testing before.
Well... if they're testing new formats, they're also doing it in conjunction with cookies. I only saw it on one of my platforms, and I couldn't make that platform go back to normal until I removed the browser's cookies. That's why I originally thought the centering was happening for everyone, because no matter what site I looked at with Adsense on it, even sites that weren't mine, the ads were centered, and it persisted for at least three hours (from when I first noticed it until I removed the cookies).
Yes, today all ads on all my sites have centered text. They look awful, give a sense of disorder and CTR is down. There's no new option to chose change the alignment in control panel. I hope they give us that option on revert back to the original format.
I posted a response to a similar thread on this topic yesterday, but in case you didn't see it, I'll repeat it here :)
The variation you noticed is part of normal and ongoing testing we perform to improve our ad formats. They only run for a very short amount of time and are only shown to a very small percentage of your users.
Our engineers are always closely monitoring the results of our test, and any variations should impact only a small percentage of your impressions.
Also, these tests are done on a user basis, not site basis, so only a very small percentage of people see the ads in these variations.