Wolfman - Twain's quote is representative of many people these days.

I'll restate my feelings on global warming....

-I don't doubt there is current warming
-I don't doubt that some portion of the recent warming is caused by CO2.
-Since one can't assume that historical relationships will work in the current situation (due to historic data showing CO2 lagging temperature, which is not seen today, or the fact that no cars or factories were around 600 000 years ago), how can we quantify the portion of the current warming that is caused by CO2?


The third point is the critical one. So far this has been estimated this through GCM's - which only consider what we tell them. GCM's are only as good as our understanding of the climate system. Nobody will say that our knowledge of the climate is anywhere near complete.

All I'm asking is how can we quantify CO2 related warming without looking at historical relationships?