[fourscoreandfree]

Recent Vostok Antarctic ice cores comprise a record of the earth’s atmosphere going back 420,000 years. Scientific analyses of these cores demolish the notion that man-made activities are responsible for global warming. There is a regularity of about 100,000 years in the peaks of CO2 and CH4 within the same range, roughly, 200ppm - 400ppm, and a lagging increase or decrease in temperatures. Man has had nothing to do with this complex multi-variable natural cycle stretching back hundreds of thousands if not millions of years. Orbital deviation is one cause. Solar variation is another. There are others yet to be fully understood.

[palmer]

There is a regularity of about 100,000 years in the peaks of CO2 and CH4 within the same range, roughly, 200ppm - 400ppm, and a lagging increase or decrease in temperatures.

That's true except it was around 200 or less to about 300 max:

Consider that the temperature rise or fall that caused those CO2 rises and falls was about 8-10C. That means each rise of about 100ppm was caused by a 10C rise in temperature. The latest rise in CO2 from 280 to 400 (and rising 2.5 per year) would have to be preceded by a 10C rise or more in temperature. That has not been the case. The natural rise from the Little Ice Age to the present is about 1C. That means the rest of the rise in the CO2 is manmade.

That manmade rise is supported by estimates of CO2 production from fossil fuel burning, cement making, etc. It is supported by very rough estimates of the natural flux. It is not proven to be manmade (proof is essentially impossible in science). But the evidence points to a manmade CO2 rise. The ongoing rise of about 25 ppm per decade would have to be preceded by natural warming of 2.5C a few hundred years ago. That is clearly not the case. Therefore the CO2 rise is manmade.

The next question is so what? That is the only question that matters, and the answer is that is doesn't matter very much how much new CO2 we add. See the chart I posted earlier in the thread showing the logarithmic effect of added CO2.