Atmospheric CO2 Over the Past 20,000 Years

Looking at the graph, estimate the length of time that it took for CO2 to go from 200 to 300 ppm.

A graph showing carbon dioxide in parts per million from 20,000 years before present to the present day. Over most of the graph, concentrations range from just below 200 to 300 until near the present day, where it shoots up to 400.
Atmospheric carbon dioxide (ppm) over the past 20,000 years.