“how does this happen?.....was it wrong info to begin with ?”
It’s all been based on computer models. Anybody who’s ever taken a basic programing course knows about GIGO, Garbage In Garbage Out. To admit that they are wrong all those programmers and info gathers will have to admit to major mistakes at the least, fraud as a middling or crimes against humanity near the top and even perhaps premeditated murder.
http://www.theguardian.com/environment/2009/nov/29/ipcc-climate-change-leaked-emails