Barbara, John,
First, thanks John, you are doing a more careful job than I would in looking up sources. You mention tobacco; the report on ExxonMobil I posted the link to a couple months ago by Union Concerned Scientists says that not only is ExxonMobil using the same tactics as tobacco companies did in the past, they are using the same people.

OK, yes, Barbara did ask interesting questions. I did not know how to refute the fact that CO2 increase leads deglaciation. So, I asked a sedimentologist who is also involved in the Santa Barbara basin paleo-climate work. He said that the CO accelerates the warming. Following what he said (my interpretation), some natural retreat in ice sheets or warming allows CO2 to increase. That increase drive more warming. Without the CO2, it might just be an oscillation and not go into interglacial.

"Isn't climate too complex, too dynamic a system for one small component, like CO2 levels, to have that much of an effect?:
Simple answer: "no". I'm sure it is known what temperature the earth would be if there was no CO2. Would be interesting to get that number (would be a model, but would give the idea).

As for "If the earth is in a natural climate [warming] change,.."
Big "if".

"These two scientists point to evidence in Greenland -- which was much warmer at the height of the last natural warming cycle than it is today -- and elsewhere."

I assume they refer to 120,000 years ago: Oxygen Isotopic stage 5e. Yes, it was probably a little warmer than today, and global sea level was about 6 m higher than today. This warm period resulted in pronounced wave-cut platforms along the uplifting parts of California Coast (as did other warm intervals; wavecut platforms are being cut today). I'd be interested if it is know that this higher global sea level was due mainly to deglaciation of Greenland, or if it was partly west Antarctic (warmer water causes a sealevel rise without melting anything, also)

So, what is the point? The problem is the rate of increase of CO2 now, and that it is now about as high as it has been in at least the last 1 million years, and certainly headed much higher.

People who want no action on global warming, or who get their information from these people, like to point out that there have been big natural climate changes in the past. True. The ones in the next 100 years may be faster than any in the past. And, there are 7 billion people who have to adapt to the changes...not a few cave men chasing the retreating ice sheet to hunt mammoth while the deserts advanced northwards.

I may not be able to participate in the rest of discussion due to lack of internet access: Chris...at JFK hotel.