Antarctic. Here's the gist of it:
It is from air bubbles that we know for sure that carbon dioxide has increased by about 35 percent in the last 200 years. Before the last 200 years, which man has been influencing, it was pretty steady. ...carbon dioxide today is not just out of the range of what happened in the last 650,000 years but already up 100 percent out of the range. The ice core record showed it used to take about 1,000 years for a CO2 increase of 30ppmv. It has risen by that much in the last 17 years alone.
If that's a natural occurrence, that's quite a coincidence. Even if it is natural, it still means that people need to decrease the amount of CO2 they put in the atmosphere. No matter where it comes from, too much CO2 is bad.