Steven Mosher
You state that “1000 ppmv is a low estimate”
This is false, Steven.
It is based on a rather optimistic estimate of the WEC of all the inferred possible fossil fuel resources on our planet.
This estimate tells us that 85% of the original fossil fuel resources are still in place (IOW we have “used up” 15% to date).
I have seen many lower estimates of remaining fossil fuels (Hubbert, etc.) but no estimates that were higher.
So this is not a “low estimate”, but rather a “high estimate”.
And it tells us that 1,000 ppmv is a most likely upper limit of atmospheric CO2 caused by human GHG emissions, not a “low estimate”.
As far as the latest Lewis/Schlesinger estimates of 2xCO2 ECS (based largely on physical observations) are concerned, I also have no reason whatsoever to believe that these are “low estimates”, just because they are at the lower end of earlier (model-derived) estimates. Science moves on and error ranges get narrowed down.
Any future projection is based on estimates, Steven.
But it is false to say that these are “low” estimates, just because you think they should be higher, without presenting any real data to back up your reasoning.
Max