The CO2 concentration in part per million since 1958. This curve is called the Keeling curve. The small wiggles are seasonal variations caused by plants going dormant in the winter, and thus using no CO2.
The Vostock ice cores have been analyzed for atmospheric CO2 content over the last 1000 years. They show fairly steady CO2 levels until the time of large-scale industrialization. The dashed portion of the curve is the Keeling curve from above.
Infrared absorption in the earth's atmosphere, showing the relative importance of water vapor vs. CO2. (AQ; Allen 1973)
Deforestation, Rondonia district, Brazil. Landsat images show healthy vegetation as red. Images were taken in 1975, 1986, and 1992. From USGS Earthshots page.