|Chart of carbon dioxide levels at Mauna Loa.|
Chart copied December 6, 2014. Levels today are at
376.66 parts per million. Click for image credit.
NOAA monitors carbon dioxide on the Mauna Loa Volcano in Hawaii. This is the best place to regularly monitor upper atmospheric chemistry in the U.S. because it is so far away from most stationary sources of carbon dioxide.
Each year, carbon dioxide goes through natural increases and decreases. During the winter and early spring months, carbon dioxide use increases in the atmosphere because the northern hemisphere plant productivity decreases during this time. It peaks about May. During the summer months, carbon dioxide levels drop and reach the nadir in September.
Here in December we are about half-way through the gradual increase trend that will conclude in May. In looking at the data here, you can see that last year on this date (December 6th) we were at 395.91ppm (parts per million) carbon dioxide. This year the level is 397.58. This is a 1.67ppm increase. Ten years ago, the level on the same date was 376.66.
It is clear that we are heading to over 400ppm this coming May and probably sooner. The preindustrial carbon dioxide levels were 280 ppm.
If you are interested, you can play with the data from Mauna Loa here. You can also read this 1959 article from Scientific American that summarizes the issue with carbon dioxide and climate.