influence from local contamination. Due to funding cuts in the mid-1960s, Keeling was forced to abandon continuous monitoring efforts at the South Pole, but he scraped together enough money to maintain operations at the Mauna Loa Observatory, which have continued to the present day. Keeling's Tellus article of 1960 presented the first monthly records from Mauna Loa and Antarctica (1957 to 1960), finding a "distinct seasonal cycle...and possibly, a worldwide rise in from year to year." By the 1970s, it was well established that the increase of atmospheric carbon dioxide was ongoing and due to anthropogenic emissions. Carbon dioxide measurements at the Mauna Loa Observatory in Hawaii are made with a type of infrared spectrophotometer, now known as a nondispersive infrared sensor, that is calibrated using World Meteorological Organization standards. This type of instrument, originally called a capnograph, was first invented by John Tyndall in 1864, and recorded by pen traces on a strip chart recorder. Currently, several laser-based sensors are being added to run concurrently with the infrared spectrophotometer at Scripps Institute of Oceanography, while NOAA measurements at Mauna Loa still use the nondispersive infrared sensor. Results and interpretation The measurements collected at Mauna Loa Observatory show a steady increase in mean atmospheric CO2 concentration from 313 parts per million by volume (ppmv) in March 1958 to 406 ppmv in November 2018, with a current increase of 2.48 ± 0.26 (mean ± 2 std dev) ppmv CO2 per year. This increase in atmospheric CO2 is due to the combustion of fossil fuels, and has been accelerating in recent years. Since CO2 is a greenhouse gas, this has significant implications for global warming. Measurements of CO2 concentration in ancient air bubbles trapped in polar ice cores show that mean atmospheric CO2 concentration was between 275 and 285 ppmv during the Holocene epoch (9,000 BCE onwards), but started rising sharply at the beginning of the nineteenth century. The Keeling Curve also shows a cyclic variation of about 6 ppmv each year corresponding to the seasonal change in uptake of by the world's land vegetation. Most of this vegetation is in the Northern hemisphere where most of the land is located. From a maximum in May, the level decreases during the northern spring and summer as new plant growth takes out of the atmosphere through photosynthesis. After reaching a minimum in September, the level rises again in the northern fall and winter