Jeff Masters of Weather Underground posted a new blog this week noting that measurements of carbon dioxide in the atmosphere show that for the first time in the last 800,000 years the carbon dioxide levels in the atmosphere reached 404 parts per million. You can read his post here.
Carbon dioxide has been measured directly since the International Geophysical Year in 1958 at a number of sites around the world, including Mauna Loa in Hawaii. But scientists have been able to determine carbon dioxide levels much farther back in time using a variety of other methods such as bubbles in ice cores drilled from Greenland and Antarctica. The graph below shows the values of carbon dioxide that have occurred in the atmosphere from 800,000 years ago on the left to the present on the right. The graph shows the characteristic saw-tooth pattern associated with the wax and wane of ice ages but none of those peaks reached much above 300 parts per million. It was only in the last 100 years (far right) that the carbon dioxide levels have risen so dramatically to their current peak. You have to go back millions of years in earth history to find another time period when there was so much carbon dioxide in the air.
Where is this carbon coming from? You can use radiocarbon dating methods to determine the age of the source of this carbon. The dating analysis has shown that the recent carbon in the atmosphere has come primarily from carbon sources that are millions of years old. The only known source of this “old” carbon is from the burning of fossil fuels, which release the “old” carbon into the atmosphere where it can be measured.
