Looking Up – Part 2: Atmospheric Carbon Dioxide

(Editor’s note: As part of nature observations columns, three monthly features will present topics related to our atmosphere and skies. This second feature addresses our atmosphere.)

Our current atmosphere, composed mostly of nitrogen (78 percent) and oxygen (21 percent) also includes a growing concentration of carbon dioxide (CO2).

That gas, although present only at a concentration of about 0.04 percent (or 400 parts per million — ppm), has been getting a lot of attention as it has been shown to act as a greenhouse gas, enveloping the Earth and increasing its temperature. CO2 has occurred naturally since the formation of the Earth, and its concentration has greatly varied over time.

For example, CO2 was present at a concentration of more than 1,000 ppm in the time of dinosaurs, when the Earth was up to 20 degrees Fahrenheit hotter than today. A small greenhouse effect is good for the earth, as it keeps some heat to sustain life, but too much heat is disruptive. The atmosphere around Venus contains 300,000 times more CO2 than Earth, and its surface temperature is 864 degrees F.

During the last 800,000 years, there have been many fluctuations in CO2 by about 80 ppm, thought to be due to changes in the Earth’s orbit; the Earth temperature variations during that time period closely match the CO2 fluctuations. More recently, in 1800, the Earth atmosphere contained about 200 ppm CO2, and this has now sharply increased to more than 400 ppm.

The increase coincides with the start of the industrial revolution, with the burning of fossil fuels releasing growing amounts of CO2. Isotope analyses also show that the historical increase in CO2 correlates to the burning of fossil fuels.

Since 1958, CO2 measurements have been taken daily on top of Mauna Loa in Hawaii, and these consistent, detailed measurements illustrate the growing CO2 concentrations from about 350 ppm in 1958 to more than 420 ppm in 2025. The undisturbed air, remote location, and minimal influence of vegetation and human activity at the top of Mona Loa are ideal for monitoring constituents in the atmosphere.

The graph shows monthly mean carbon dioxide representative of Earth’s atmosphere average concentration. Besides the obvious trend in increased concentrations, the graph also shows the annual, seasonal change of CO2 concentration in dry air due to the vegetation growth: the reason for the seasonal changes in the curve is related to the unequal distribution of land and ocean in the Northern and Southern Hemispheres.

There is a lot more land (and thus area for plants to grow) in the Northern Hemisphere than in the Southern Hemisphere, so when the Northern hemisphere plants are actively growing in April through September, they are removing CO2 from the atmosphere, lowering the concentration. At the end of the Northern Hemisphere growing season, plants go dormant and CO2 starts to build up again.

Since there is less land and less area for plants to grow in the Southern Hemisphere, they can’t keep up with the loss of activity from the Northern Hemisphere plants, and CO2 increases overall. The Keeling curve data is also matched by measurements in Samoa, Barrow (Alaska) and the South Pole. About half of the CO2 that humans release into the air stays in the atmosphere. The other half is absorbed at Earth’s surface, split roughly equally between land and ocean.

Increases in temperatures will result in increased sea levels, increased droughts and other significant weather events. Decreasing the use of fossil fuels and associated CO2 releases will reduce the impact on earth’s climate. With abundant solar, wind and geothermal energy potential in New Mexico, low-emissions energy sources can provide a partial solution to the threat on our climate.