Atmospheric carbon dioxide has been monitored since 1958 at NOAA’s Mauna Loa Atmospheric Baseline Observatory in Hawaii. Values cycle up and down due to the amount of green vegetation available to convert CO2 to O2 by photosynthesis. Plants of the northern hemisphere reach maturity in June-August and reduce the level of CO2 from the previous month. Decomposition and respiration returns carbon dioxide to the atmosphere in the fall and winter. This is known as the fast carbon cycle. The carbon cycle of earth is discussed fully here.
The mean value of CO2 for May 2019 set the highest level in 61 yrs. This chart shows the monthly values plotted for the recent 5 years.
The full record for the Mauna Loa Observatory clearly shows the seasonal and long-term trends. The long-term rate is increasing evidenced by the greater steepness of the plot. More charts and analysis are available at this link.
NASA Earth Observatory posts a blog Earth Matters. The 14 June 2019 post by Adam Voiland clearly lays out the situation faced by the growth of CO2 in the atmosphere. Please read it for the full story. Here are highlights if you are short on time.
Rate of Increase is Accelerating
In the 1960s, the increase was about 0.8 ppm per year. The 1980s and 1990s showed it was 1.5 ppm year. It is now more than 2 ppm per year.
There is “abundant and conclusive evidence” that the acceleration is caused by increased emissions, according to Pieter Tans, senior scientist with NOAA’s Global Monitoring Division.
Very Long-Term Records
Detailed records of trapped air bubbles in ice core samples from 800,000 yrs ago show the atmospheric levels have never been this high. Our modern age driven by fossil fuel use is the culprit.
The non-uniform global distribution of vegetation and the seasonal cycles of plants causes the levels of CO2 to be patchy around the globe. In the northern hemisphere, springtime gives us the highest concentration peaking in May. The photosynthesis by plants draws down the levels for several months before it begins to rise again. Continued fossil fuel use keeps pumping more CO2 into the atmosphere than the vegetation and oceans can process. Hence the increase over time.
Mixing Does Occur Seasonally
Oceans Play a Significant Role
Oceans are also sinks for CO2. Phytoplankton convert it to O2. But, the process operates on a longer time scale than the atmosphere. Early research suggests the oceans might slow down their absorption of CO2 over time leading to greater acidification and impact on marine organisms. More CO2 would be left in the atmosphere. A lengthy article outlining studies on this topic is available at this link.