SOURCES: 1) The amount of carbon dioxide in our atmosphere has been increasing rapidly over the last few decades and continues to do so. 2) Historically, the trends in increase of carbon dioxide started in the late 1700's. This was the approximate time of the Industrial Revolution. At this time, the carbon dioxide concentration was around 270 ppm (pounds per million). Concentrations grew very slowly from this time until the twentieth century. But in the last century, especially in the last fifty years, carbon dioxide levels have grown rapidly. It is presently around 350 ppm.