The Mauna Loa atmospheric CO2 measurements constitute the longest continuous record of atmospheric CO2 concentrations available in the world. The Mauna Loa site is considered one of the most favorable locations for measuring undisturbed air because possible local influences of vegetation or human activities on atmospheric CO2 concentrations are minimal and any influences from volcanic vents may be excluded from the records. The methods and equipment used to obtain these measurements have remained essentially unchanged during the 47-year monitoring program.
Because of the favorable site location, continuous monitoring, and careful selection and scrutiny of the data, the Mauna Loa record is considered to be a precise record and a reliable indicator of the regional trend in the concentrations of atmospheric CO2 in the middle layers of the troposphere.
The Mauna Loa record shows a 19.4% increase in the mean annual concentration, from 315.98 parts per million by volume (ppmv) of dry air in 1959 to 377.38 ppmv in 2004. The 1997-1998 increase in the annual growth rate of 2.87 ppmv represets the largest single yearly jump since the Mauna Loa record began in 1958. This represents an average annual increase of 1.4 ppmv per year. This is smaller than the average annual increase at the other stations because of the longer record and inclusion of earlier (smaller) annual increases.