During the week of May 13th, the CO2 level at the Mauna Loa Observatory in Hawaii topped 400 ppm repeatedly. Daily levels of CO2 can vary due to weather, and there are seasonal trends as well.
Using Cave Formations to document Ancient Climate
A geochemist at the University of Minnesota is a pioneer in the use of cave formations to document ancient climate. Stalagmites are being looked at as a collection of climate sensors (like tree rings), extending often hundreds of thousands of years back in time. This work is providing the scientific community with an increasingly precise time scale.
For more details on this work, see the complete article at http://www.smithsonianmag.com/science-nature/The-Secrets-of-Earths-History-May-Be-in-its-Caves-183829981.html
