For context, this is one of my favorite climate graphs, showing 800,000 years of atmospheric CO2, including the massive run-up over the past century. We're now around 420 parts per million (ppm), more than anytime in 800,000 years (actually more than anytime in the past 5 million years) and completely outside the natural ups and downs in the record. This is the driver of the current #climate crisis.
@petergleick It is striking. Now, it's entirely possible that we'll find some calibration factor that massively changes the ice core numbers: this would be used as a "ACC isn't real" rallying point. The most stark section for me is from 1950 onwards where we have reliable data.
@dvavasour The ice core data are tremendously well vetted. Look for Vostok core papers on Google Scholar (or equivalent) for details. Here's a bit of background.
https://cdiac.ess-dive.lbl.gov/trends/co2/vostok.html
Historical Carbon Dioxide Record from the Vostok Ice Core

Carbon Dioxide Information Analysis Center