04/30/2014 11:19 am ET Updated Dec 06, 2017

Monthly Carbon Dioxide Concentration in our Atmosphere Will Surpass the 400 ppm Threshold in April

April 2014 will become a month of infamy in the climate change story. Once the numbers for April are crunched by NOAA and Scripps Institute, it will be the first time in human history that the monthly average carbon dioxide concentration in our atmosphere will be confirmed to exceed 400 ppm (actually, it will exceed a level not seen for 3 million years). Last year, media reported that we squeaked across the 400 ppm threshold, but subsequent analysis by NOAA revised the number downward to a fraction of a point below the historic level.

The longest continuous instrumental record of CO2 data is being collected atop the Mauna Loa volcanic peak in Hawaii. Dave Keeling set up an Infrared Analyzer on the peak in 1957. Surrounded by thousands of miles of ocean, this location provided a pristine undisturbed atmosphere. It was devoid of human interferences since it was well isolated from heavily industrialized continents. On the first day of measurement in March 1958, Keeling recorded an atmospheric CO2 concentration of 313 ppm.


Keeling subsequently observed his measurements increase to a maximum in May, then decline to a minimum in October. The CO2 concentration then repeated the same seasonal cycle the next year. Keeling observed that "We were witnessing for the first time nature's withdrawing CO2 from the air for plant growth during summer and returning it each succeeding winter." Planet Earth appeared to be breathing.

He made another significant observation. The average CO2 concentration in 1959 was higher than the previous year. In 1960, the average concentration had increased still further. Even with this limited data, he published his findings noting two profound conclusions:

• Our planet is undergoing natural seasonal breathing
• The background atmospheric concentration of CO2 is increasing

In the figure below, I have adapted a graph from NOAA and inserted actual numeric data (as well as my own "X" April 2014 prediction) to illustrate this seasonal breathing. To observe this seasonal breathing, look at the data point for October 2011. The atmospheric CO2 concentration was 388.96 ppm. Now, count each data point month-by-month (Nov, Dec, Jan, Feb, Mar, Apr, May). You will see the plot reach a maximum at 396.78 ppm in May 2012.


In May, vegetation is springing to life in the northern hemisphere. Photosynthesis will begin to sequester CO2 as plants sprout and leaves grow. Continue following each data point month-by-month and you will reach a minimum in October 2012. Photosynthesis slows down, leaves begin to fall, and vegetation eventually falls dormant. CO2 concentration once again rises through the late autumn, winter, and early spring months.

You can see the seasonal pattern. Looking at the 399.65 ppm reading for March 2014, it is easy to extrapolate one month forward. The monthly average for April 2014 will surely exceed 400 ppm. You will be able to confirm this value once NOAA and Scripps analyze the data and report it here, probably during the first week of May. The Keeling Curve has become an icon of the global warming story and serves as the cornerstone of global warming science today.

NOAA, Scripps, and others around the globe are gathering high precision, high accuracy scientific data confirming our human contribution of greenhouse gases to the atmosphere. The consequences of our actions have been compiled and conveyed in recent IPCC Assessment Reports. The 400 ppm threshold should be a sobering wake-up call. It is time for us -- individuals, business leaders, and our policy makers -- to accept the science and face the civilization challenging issue of climate change.