Short answers, pulled from the story.
The Keeling Curve is a graph of the continuous measurements of atmospheric CO2 taken at the Mauna Loa Observatory in Hawaii from 1958 to the present. Naomi Oreskes, Professor of History of Science at Harvard University, has called it one of the most important scientific works of the twentieth century. Many scientists credit it with first bringing global attention to the accelerating rise of CO2 in the atmosphere.
Charles David Keeling, a scientist at the Scripps Institution of Oceanography at UC San Diego, created the Keeling Curve. He began continuous measurements at Mauna Loa in March 1958 and supervised the monitoring program until his death in 2005. His son, Ralph Keeling, has led the project since then.
Mauna Loa was selected because of its remote location far from continental landmasses and its complete lack of vegetation, both of which reduce contamination of atmospheric readings. Keeling and his team measured the incoming ocean breeze above the thermal inversion layer to further minimize interference from the volcano's own vents.
Measurements show mean atmospheric CO2 rose from 313 parts per million in March 1958 to 406 ppm in November 2018, increasing at roughly 2.48 ppm per year. On the 9th of May 2013, the daily mean concentration at Mauna Loa surpassed 400 ppm for the first time, a level not seen since the mid-Pliocene, 2 to 4 million years ago.
The annual wave of about 6 ppm reflects the cycle of plant growth and decay. CO2 falls from a May peak through the northern spring and summer as photosynthesis draws carbon from the air, reaches a minimum in September, then rises again in fall and winter as plants die and release CO2. Most land vegetation sits in the Northern Hemisphere, so its seasonal rhythm drives the global pattern.
In 2015, the American Chemical Society designated the Keeling Curve a National Historic Chemical Landmark. Commemorative plaques were placed at both the Mauna Loa Observatory in Hawaii and at the Scripps Institution of Oceanography at the University of California, San Diego.