Of what? Temperature or CO2 concentration? If you have a reference, tell me: I wouldn't be able to find this easily with a Web search.
Your link notes this:
"The extension of the Vostok CO2 record shows the present-day levels of CO2 are unprecedented during the past 420 kyr."
which is rather obvious. They probably make the assumption that the numbers are reasonably accurate and that the uncertainty bounds are low probability, which is statistically reasonable.
But did human activity cause the CO2 and temperature increases 340,000 years ago ?
Of course not. A warming global climate caused the CO2 increases 340,000, 240,000, and 130,000 years ago, and also about 10,000 years ago at the end of the last glacial period. After which CO2 concentrations remained relatively stable until a few years into the 1800s. Also note that the Vostok ice core data define a CO2 concentration zone that has only been exceeded (due to anthropogenic emissions) in the past two centuries.
That's the problem that's keeping climate scientists hot and bothered -- what happens to the climate when one of its controlling factors jumps out of its normal range by so much, so fast? And that's hard to predict.
Now I have to get back to AG.
Why not both- --- I don't have a reference, but started thinking about this when I saw the links about the CO2 lagging the temperature by several thousand years.
The accuracy may be discussed in one of the global warming links, but I have only recently been scanning/reading them and have not covered them in detail.