[tuzo29]

The problem I have with this chart and other charts purporting to show long term climate trends is the assumption that the extrapolated historical data is an accurate reflection of reality at the time. I would guess that "ice core data" is derived based on multiple assumptions concerning rate of accumulation and methods of interpretation - leaving room for introduction of biases whether conscious or not. Also, is the modern data based on ice cores? If, as I suspect, it's based on measurements by modern instrumentation then can it properly be compared to estimations from ice cores?

I said ignore the projections. When you look at ppm it's an absolute measurement. If there's 400 ppm, it means that 0.04% of the air is CO2. The ice cores have air in them. (http://www.antarcticglaciers.org/glacier...re-basics/) "Ice coring has been around since the 1950s. Ice cores have been drilled in ice sheets worldwide, but notably in Greenland[3] and Antarctica[4, 5]. High rates of snow accumulation provide excellent time resolution, and bubbles in the ice core preserve actual samples of the world’s ancient atmosphere[6]." They measure the proportion of CO2 in the air. This does not require a fancy model and calibration. Just take the air from the ice and run a chemical analysis.

It amazes me how skeptical the general public is about scientific processes. Most of them aren't nearly as complex or unreliable as people think. Despite popular belief scientists aren't nefarious and/or stupid (in general). They search for facts and the truth. It seems that this is where the major difficulty is. Believing scientists are searching for the truth and keeping tabs on each other along the way, so that the rest of us can take their word for what they find. It seems to me that when people see data that doesn't match their prior beliefs, they just disregard it. Like all those people who didn't believe Galileo.
(sarcastic aside: Really there is a secret global organization of scientists working on a taking over the world with a new international program to brainwash us all. Please go read 1984 for the details of how they are going to do it.)