An official website of the United States government
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
 Image Number K3829-14 |
Range scientist Herman Mayeux checks a light-sensing bar that indicates solar radiation levels within plastic growth tunnels. Carbon dioxide concentrations inside the tunnels range from today's 350 parts per million to the 200 ppm present during the last ice age.
Photo by Perry Reich.
