You've misread the wikipedia article. What's remained constant is the fraction of (human) emitted CO2 which remains in the atmosphere and the fraction which is

You've misread the wikipedia article. What's remained constant is the fraction of (human) emitted CO2 which remains in the atmosphere and the fraction which is absorbed by oceans and other sinks. For what you've said to hold true would require both anthropogenic and natural sources to be rising in lock-step.