The carbon dioxide concentration in the atmosphere at Mauna Loa Observatory in Hawaii on May 5 was 403.95 parts per million. The reading April 4 was 402.45. One month prior to that (March 5) the reading was 401.16.

May 5 — 403.95
Apr 4 — 402.45
Mar 5 — 401.16

Carbon dioxide holds heat and moisture in the air. It is a major cause of the warming of our planet. Measurements are taken daily by scientists with the Scripps Institution of Oceanography. For more information go to

The graph below (©Scripps Institution) shows the growth of CO2 in our atmosphere from 1960 to the present.