I suspect that we are mostly in agreement but are not reading English the same way. What I said about Joe, a generic guy, his lawnmower, a generic emitter of CO2, gasoline, a generic source of carbon to burn, and NYC, a generic city highly interested in CO2 and pushing carbon taxes, were all generic examples; looks like I should have had a prefix of "such as".

But my main point was that the lecture was talking about wildly different scales than what we are seeing on Earth now or likely for, say, the rest of this century. Or, the lecture was talking about really extreme, very different, conditions -- due to a cooler sun and the earth's orbit -- over 800,000 years to many millions of years. Heavily he was discussing geology, that is, a science of really slow changes, from volcanoes, huge swings in the chemistry of the air and water of earth, etc.

For your "billions of tonnes of carbon per year", I don't know what to think about that, that is, I don't know what to compare it with so don't know if that amount is, for all of the earth and sources of CO2, methane, etc. just a tiny, insignificant, nearly invisible drop in the total bucket or a major change. E.g., I have yet to see good data on how much CO2 and/or methane comes from volcanoes, on land and in the oceans, year by year. E.g., how much CO2 is dissolved in the upper, say, 2000 feet of the oceans, and if the temperature of that water is increased by, say, 1 degree C, how much of that CO2 will escape into the atmosphere? My point here is, I'm short on information to evaluate the quantities involved here, e.g., your "billions".

It was an interesting talk, e.g., with lots of really cute chemistry -- I wish my chemistry courses had had that much depth. I can see how geologists, e.g., in the AGU, could get really involved. Or, the lecture should be really popular on some Web site like HN but GN for Geology News!

But I see very little relevance in that lecture for the current intense discussions leading to carbon taxes, etc., which seem to be of high concern on HN.

E.g., if the sun gets 30% cooler, then we might want to review the lecture, if anyone is still here! Or, if the earth has an orbit situation such as in the several cases of global cooling that show in the ice cores from 800,000 or so years ago, then maybe we should rush to add all the CO2 to the atmosphere we could and otherwise risk big ice sheets in Kansas, Texas, Panama, or some such?

But these cases, along with the big asteroid hit of 65 million years ago, the huge volcanoes of the Russian traps, when India moved north, hit South Asia and pushed up the Himalayas, even when Yellowstone blew and put, IIRC, ash 1000 feet deep 1000 miles down wind, are super major biggie causes of disaster, and, of course, if a gamma ray burst popped off somewhere in our part of our galaxy, as far as I can tell, that make everything humans are doing now just an invisible, trivial nit.

From all I've seen, if we want to talk about human sources of CO2 and their contributions to significant global warming for the rest of this century, then we have a lot of really hard work to do.

Why?

(1) A lot of work was done trying to predict what the realistic CO2 levels would do to global temperatures, and now we can see that nearly all the temperature predictions from that work were way, way too high.

(2) In a sense, we know too much: E.g., we know that the fluid flows, both in the atmosphere and the oceans, satisfy the Navier-Stokes equations of fluid flow. So, first cut, we would have to solve those equations for the surface of the earth, on both land and the oceans. And we would have to include the effects of all the solar and infrared radiation involved. Then, even to get started, we would need the current initial conditions, e.g., what the volcanoes were doing, and we are a long way from knowing those. Then, we would be very short on a suitable computer.

Sure, we'd like to take an approach easier than (2), but as in (1) that easier approach was nearly all wildly inaccurate. With (2), we are stuck, or stuck-o.

But the lecture had some amazing geology and chemistry!