ppmv

Specifically, CO2 concentrations have peaked at around 300 ppmv during the 150,000 year cycle, but are currently at around 383 ppmv.

I wouldn’t be surprised if you can convert the 400 ppm CO2 value into ppmv and that it comes out to around the 280 ppmv CO2.

Both exceed 100% because their CO2 values were increased to 345 ppmv, without changing their other constituents to compensate.

Surprisingly, this raises the CO2 threshold for glaciation to a staggering 3000 ppmv or so.

Fun fact, C3 plant life dies at 220 ppmv or lower CO2.

Slapping an atmospheric CO2 value in ppm onto a graph taken from a study that measures CO2 values in ppmv from ice cores isn’t science.

Recent studies agree, however, that doubling the carbon dioxide concentration from the pre-industrial level of 270 ppmv will probably increase global mean temperature by 1.5°C to 4.5°C (47, 48, 49)—but most likely by 2°C.

From abstract: These data suggest present-day CO2 (412 ppmv) exceeds the highest levels that Earth experienced at least since the Miocene, further highlighting the present-day disruption of long-established CO2 trends within Earth’s atmosphere.

In fact the absolute concentrations are not especially important, as the temperature response to increasing CO2 concentration is logarithmic - a doubling from 500 to 1000 ppmv would have approximately the same climatic effect.

Ok so I think the parameter you want to be looking for is the temperature (not necessarily at altitude) that results in some particular amount (ppmv) of water vapor at altitude.

Some numbers I've pulled out of various places (not guaranteeing these are accurate): Earth's atmosphere is 5e18 kg, 99% of mass of atmosphere is below 30 km (so mass above that is 5e16 kg), lifetime of gas in upper stratosphere is ~8 years, concentration of water vapor there is about 7 ppmv.

Here's where we are headed at present I think, just a question of how fast: > "Carbon dioxide concentration during the mid-Pliocene has been estimated at around 400 ppmv...

Actually, for these 400.000 years that preceed 1750, the atmospheric CO2 concentration has oscillated between 200 and 280 ppmv (graph below)." Source: Petit & al, Nature, June 1999 We are impacting the climate in a way that would take decades to appreciate the impacts.