This line graph has as its horizontal axis the year from 900 to 2000, and its vertical axis represents carbon dioxide concentrations in parts per million by volume, ranging from 260 to 380. The early data was obtained by ice cores while the more recent values were obtained through direct measurements. The general trend shows a rise in carbon dioxide concentrations over time, with quite a sharp increase beginning in the mid 1800s; wherein, the concentrations from 900 to the early 1800s stay around the 280 parts per million by volume, after which they begin to increase reaching around 340 parts per million by volume in the late 1900s.