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.