Hello Jo and Cooper
I would say that he's probably UT for his naps and you should push out his A time. At 8 months, most LOs are doing 3-4h A times (see here:
http://babywhispererforums.com/index.php?topic=64158.0). I would add 10-15 minutes to his A time every 3 days (so give him 3 days for his body to get used to the new A time before trying more). If the jump is too much, he will get OT, and that's not fun to clean up.
It's true that he's becoming more aware of his surroundings, but I think this is a simple case of him needing more A time
Also, if you find his days get too long with the increased A time, I would start capping his first nap (maybe to 2h, which is still a very, very nice long nap that will keep him happy).
HTH!