It not a logical conclusion, unless the CO2 increase precedes the warming, but historically, it follows. See:http://www.grida.no/climate/vital/graphics/large/2.jpg 
I'm afraid it does "logically" follow--it just hasn't been indubitably proved yet. We're spewing out CO2 and cutting down the forests that soak it back up. CO2 is increasing. CO2 acts as a greenhouse. The temperature has gone up. Thus . . .
You misread my post. I said longer-term climate change does NOT mean that people can NOT possibly have affected things. The two are separate issues.
It not a logical conclusion, unless the CO2 increase precedes the warming, but historically, it follows. See:http://www.grida.no/climate/vital/graphics/large/2.jpg
"We're spewing out CO2 and cutting down the forests that soak it back up. CO2 is increasing. CO2 acts as a greenhouse. The temperature has gone up. Thus .
Actually we (US) are not cutting down much forest. Furthermore, more carbon is soaked up after the forest is cut down since new growth uses more carbon than old growth. There was also a recent article that suggested that forests actually contribute to warming.
IMO, there are the 3 uncertainties about global warming.
1. Is the planet getting warmer?
2. If it is warming, is man responsible?
3. If #1 is true, is it good or bad?