[cogitator]

There is no science to back that up and plenty of hypotheses of how large CO2 increases can happen,

Like what? Remember, we're looking for a wholly natural mechanism that would increase atmospheric CO2 by 80-100 ppm in 150 years. If you can show me a reference to anything that is even suggested as being able to do that, count me stunned.

Now, I will admit that they should probably note the time-scale of the measurements in the ice cores when they talk about the data. But there aren't fast mechanisms that would cause such a big CO2 excursion -- unless you'll be able to surprise me with one.

[palmer]

Remember, we're looking for a wholly natural mechanism that would increase atmospheric CO2 by 80-100 ppm in 150 years. If you can show me a reference to anything that is even suggested as being able to do that, count me stunned.

So you're pretty sure it wouldn't exist even without all your assumptions (150 year carbon cycle, etc).

But there aren't fast mechanisms that would cause such a big CO2 excursion -- unless you'll be able to surprise me with one.

There are undoubtedly fast natural processes that will create sharp albido changes, temperature changes, etc which, without making prior assumptions, could cause large CO2 changes.

[Fraxinus]

The big proof of the major probably human induced shift in CO2 concentrations is to be found in Archeology. The base line for C-14 dating is 1950, and if you take new charcoal and have it dated you will get a fairly ancient date because due to the burning of very old carbon deposits (many of which have been underground for over 300 million years) the concentrations of C-14 have dropped significantly. The correction curves also show that there have been times when the C-14 concentrations have dropped before (although I do not think anywhere near as dramatically).