the good thing about science is it's self correcting.
better estimates come by doing more science. real science builds on itself.
or we could just go by: "they said in 1989 this -- therefore no" and never question it.
that's not science.
all the actual science that's been done since, and is still being done every day, points towards the theory of agw. if you could prove otherwise, it would be a revolution, probably nobel prize worthy.