"temperature is inferred from ratios of isotopes."
I don't know what that's about.
"Therefore, if this photosynthetic temperature dependence accounts for CO2 temperature dependence, I'd expect to see CO2 concentrations go down as temperatures rise. The Vostok data"
I'd really have to read much more about this. That link leaves much out.
'Further, I don't see how to conclude anything other than that photosynthetic temperature dependence doesn't account for the CO2 variations with temperature."
It does in real life. In the summer it goes down, and in the winter, it goes up. Forests are a major sink.
"As I've been at pains to make clear, he doesn't mention it because it's not material to his argument. However, as you're evidently using it as an argument *against* CO2 caused temp increases, let's discuss it."
Whatever he's got there is irrelevant to GW. It did not use any of it "against" temp increases from CO2. I said the range of CO2 there will not result in measurable temp changes. That's true.
"As far as I know, no one says that heat being retained in the CO2 accounts for temperature increases. That would be ludicrous because the gas is not insulated from the rest of the atmosphere."
Sure they are. That's the mechanism for atmospheric heat retention. All polar molecules absorb certain wavelengths of radiation. CO2water and methane are polar. The diatomic elemental gases are not. Photons come in and get absorbed by the polar stuff. That causes them to vibrate and rotate. They bang into other stuff and there's an energy transfer. Those polars can reabsorb more photons coming in from the Sun. There's an equilibrium exchange all through the atmosphere, and it includes what eventually gets lost into space. The loss into space is due to the Earth being a black body radiator. The whole GW thing is about this process. The Sun emits, the Earth absorbs and reflects, andemits according to temperature. In order to get 2o temp changes, the CO2 concentration must triple, or more. Just moving by +/-17%, as in that link is nothing.
"temperature is inferred from ratios of isotopes."
I don't know what that's about.
Here's some articles on the subject that can help in understanding what they do:
Since molecules made up of differing isotopes of the same elements have different masses, natural processes tend to favor some molecules over others in depositing them in snow, rain, incorporating them into plant tissues etc.
The ratios of these Oxygen isotopes can be used as an indirect measure of temperature and humidity/precipitation for example, as the rate such is deposited is dependent on these factors.
Other isotopes such as 10Be & 14C are created in nuclear interactions between cosmic rays and atmospheric nitrogen, since the geomagnetic field shielding the earth from cosmic rays is modulated by solar magnetic fields such isotope concentrations vary with the solar activity cycle and thus are indicators of solar factors on the climate such as solar brightness & other impacts on the atmosphere through ionization like cloud formation.
Using mass spectrometers, vary small concentrations can be measured and used to create proxies for the variables involved with creation and depositing of these isotopes in the geological record.
I don't doubt it. But they cannot be a dominant contributor globally unless the Vostok data are wrong. The fellow is saying that the oceans are the dominant sink, that their efficiency is temperature dependent and that variation accounts for the historical CO2 concentration record.
Sure [CO2] [is not insulated from the rest of the atmosphere]
No it isn't as you yourself note: they bang into other stuff and there's an energy transfer. Consequently heat will flow from the CO2 to the other atmospheric gases. By my calculation, the N2 and O2 in the atmosphere will take up about 2000 times the amount of heat as the CO2 given the relatively minute amount of CO2.