Atmospheric CO2 Trends in Mauna Loa MMD

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This dataset contains the Monthly Mean Data (MMD) regarding atmospheric CO2 trends in Mauna Loa, Hawaii, from March 1st, 1958 till June 30th, 2017. It contains estimated data for every single month during the given period in Mauna Loa at county level.

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This dataset is sourced from the US Government’s Earth System Research Laboratory (ESRL), Global Monitoring Division (GMD). The study under discussion comprises the Mauna Loa Monthly Mean Data series (which has the longest continuous series since 1958).

In 1957 Dave Keeling, who was the first to make accurate measurements of CO2 in the atmosphere, chose the site high up on the slopes of the Mauna Loa volcano because he wanted to measure CO2 in air masses that would be representative of much of the Northern Hemisphere and hopefully the globe.

Data are reported as a dry air mole fraction defined as the number of molecules of carbon dioxide divided by the number of all molecules in air, including CO2 itself, after water vapor has been removed. The mole fraction is expressed as parts per million (ppm). For Example, 0.000400 is expressed as 400 ppm.

The concentration of a gas is defined formally as the number of molecules per cubic meter. This measurement aims to quantify how much CO2 has been added to, or removed from, the atmosphere. The concentration does not give that information because it primarily depends on the pressure and temperature, and secondarily on how much the relative abundance of each gas has been diluted by water vapor, which is extremely variable. Only the dry mole fraction reflects the addition and removal of a gas species because its mole fraction in dry air does not change when the air expands upon heating or upon ascending to higher altitude where the pressure is lower nor does it change when water evaporates, or condenses into droplets. Here is an example to highlight the importance of this phenomenon: The amount of CO2 is higher in the Northern than in the Southern Hemisphere as a result of the combustion of coal, oil, and natural gas. The measurement of this difference gives us crucial quantitative information about the emissions and removals of CO2. The concentration change produced by the addition of water vapor can be greater than the CO2 difference between the two hemispheres. In contrast, the difference in dry mole fraction does reflect the differences in emissions and removals between the hemispheres.

The last year of data is still preliminary, pending recalibrations of reference gases and other quality control checks. The Mauna Loa data are being obtained at an altitude of 3400 m in the northern subtropics, and may not be the same as the globally averaged CO2 concentration at the surface.

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Spatial Coverage

Mauna Loa, Hawaii


John Snow Labs; Earth System Research Laboratory;

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Source Citation

Dr. Pieter Tans, NOAA/ESRL and Dr. Ralph Keeling, Scripps Institution of Oceanography.


CO2 Trends, Atmospheric CO2, CO2 Concentration, Dry Air Mole Fraction

Other Titles

Mauna Loa Time Series about Atmospheric CO2, Mauna Loa CO2 Trends from 1958 till Present, Monthly Mean Data over Atmospheric CO2 Trends in Mauna Loa

DateRefers to the specific date when the specific data is
Decimal_DateThe decimal date format represents a raw date in years-only format in which the months and days are converted to partial years.numberlevel : Nominal
Average_CO2The monthly mean CO2 mole fraction determined from daily averages. If there are missing days concentrated either early or late in the month, the monthly mean is corrected to the middle of the month using the average seasonal cycle. Missing months are denoted by -99.99.numberlevel : Ratio
Interpolated_CO2It identifies the values from the average column and interpolated values where data are missing. Interpolated values are computed in two steps. First, the calculations for each month the average seasonal cycle in a 7-year window around each monthly value are done. In this way the seasonal cycle is allowed to change slowly over time. Then the trend value for each month by removing the seasonal cycle is determined; this result is shown in the trend column. Trend values are linearly interpolated for missing months. The interpolated monthly mean is then the sum of the average seasonal cycle value and the trend value for the missing month.numberlevel : Ratio
CO2_TrendIt normally referred to the values that represent the long-term movement in a cyclical context.numberlevel : Ratio
Number_of_DaysNumber of daily averages in the month.numberlevel : Ratio
DateDecimal DateAverage CO2Interpolated CO2CO2 TrendNumber of Days