Well of course, all the time. But in particular World Climate Report claims to be the webs longest running climate change blog (we'll leave aside the fact that it doesn't allow comments - how odd, I wonder why? - and so isn't really a blog). And indeed their archive goes back to March 2004. But. Try the Wayback machine on them and something interesting emerges. Up until Feb 2005 they appear to have been a redirect to www.co2andclimate.org (which *was* a greening earth soc page, but now bizarrely seems to have morphed into a site selling holidays in Spain!).
Now WCR started off as a paper based thing (I remember cos they sent me the first few issues) in 1995 or so. The end of the archive seems to be May 2003. So there is some kind of gap there.
Aha! Even better, the March 2005 version (the first updated one, according to the wayback) only has the archive going back to July 2004. By April, magically, archives back to March 2004 had appeared! Such fun.
On a side note, I'm intrigued that you consider the definition of 'blog' to incorporate 'allows comments'. There can be very good reasons for disabling comments: I can think of at least one female blogger who ended up restricting feedback to personal email from her friends purely because of the unwelcome nature of some of the stuff that was being posted to her; moreover, the great Warren Ellis has been known to close the comment form on his Wordpress blog for long periods, to shut out outbreaks of fractious behaviour.
World Climate Report may be a blog-o-crap, but a blog it remains, regardless of whether the public get a right to reply.
In an internet forum "discussion" on AGW I once had one contributor going all WCR on me.
He'd copy pasted, not QUOTED, arguments from WCR to our discussion, with the effort of trying to undermine the scientific consensus position on global warming.
After some time, one poster noted the source of this person's arguments. They weren't his own, but directly copied from WCR.
I had such fun when this was discovered, and also, when I found that Pat Michaels (whom I had previously often ridiculed in the discussion) was the chief editor of said blog.
IIRC Jorn Barger was the first person to coin the term "weblog" which was just a publicly available list of links and brief descriptions/comments to pages & sites that the blogger found interesting - so others could see them (his site is http://robotwisdom.com/). That definition's obviously changed and the name's tended to be shortened.