Who says that the 1990s was to early? It wasn't. In fact, the 1980s would have been better. And the 1970s even better. The required actions would have been much easier.
There was a scientific controversy in the 60's and 70's about whether cooling from particulates or warming from CO2 would predominate, though most scientists even then were worried about the rise in CO2. When we began to regulate particulates, it became clear that global warming was the bigger threat and scientists by 1980 were recommending we cut our greenhouse emissions. We would be in much better shape today if our politicians had listened.
No matter how much carbon dioxide has been added to the atmosphere, we will always be able to make things worse by adding more carbon dioxide.
The 1990s were not too early to act on AGW. If Canada and the U. S. had ever intended to meet their Kyoto targets, we would have had to start in the 1990s. The reason why we had to 2012 to reach the targets is that it would have taken that long to meet these targets.
Actually, I think even the 80s was too late to have an immediate impact and by the 90s, we had already caused enough AGW to go beyond 2050
