Atmosphere CO₂ Concentrations: History, Fact and Mitigation Methods

Introduction

Fig. 1: The Keeling curve. [3] (Courtesy of NOAAM)

After the invention of the internal combustion engines in the late nineteenth century, there was an increasing number of people using automobiles powered by gasoline. The level of CO₂ started to build up, with a faster speed year by year, and is still accumulating right now. Currently, global CO₂ concentration has reached a historical peak of 424 ppm. [1] According to the IPCC, the global surface temperature between 2011 and 2020 was about 1.1°C higher than it was between 1850 and 1900. [2] The observed warming is attributable to greenhouse gases, mostly CO₂ and methane, and is human-caused. [2] CO₂ emissions play a huge role in climate change, and we need some actions to reduce CO₂ in order to address climate change. A combination of personal behaviors and technologies can be used together.

History of the Keeling Curve

In 1958, Keeling initiated the following experiment: He used four gas analyzers (Antarctica, Hawaii, California and his lab) to collect and analyze samples of air from different places. [3] He then compared the partial pressures of CO₂ in collected samples to that in prepared mixtures of CO₂ in nitrogen gas. [3] The concentration of CO₂ was then determined. For years, scientists have been tracking CO₂ data using this established method and a curve is generated to document CO₂ concentrations with respect to time. This is the well-known Keeling Curve, shown in Fig. 1.

Facts of the Keeling Curve

The Keeling curve shows that CO₂ concentrations increased by 30% between 1958 (when the records began) to 2022. The x-axis of Fig. 1 represents time and the y-axis represents CO₂ concentration. The black line shows the general trend of CO₂ concentration. It may be seen to be slowly building up: from 313 ppm (in 1958) to 420 ppm (in 2022).

One interesting thing to notice is that the Keeling Curve is neither straight nor curved, but zigzag. [4] This phenomenon is called seasonal variation. During spring and summer when trees and flowers in the northern hemisphere leaf out, CO₂ is fixed in the plants and this brings the CO₂ level down. [5] During autumn and winter when the plants die, CO₂ is released back into the atmosphere, and this brings the level up again. [5] The natural annual cycle of plants creates the seasonal variation and zigzag lines on the Keeling curve.

Mitigation Methods of CO₂

Personal Behaviors: There are a lot of things we can do in our everyday lives that can help reduce CO₂ emissions. Personal awarenesses and actions is one of the solutions. For instance, turning off the lights when not using them can help reduce energy usage and reduce CO₂ emissions. Switching to energy-saving appliances in buildings is another solution. One study on energy consumption of fluorescent vs LED lights shows that LED lights save up to 22% of electricity. [6] Tons of CO₂ emissions are created during the process of getting electricity, so the less energy used, the less CO₂ emitted. What's more, we can also grow more plants because they are natural carbon sinks. More plants can also make our lives more relaxed and enjoyable!

Technologies: Direct Air Capture (DAC) might be one method to reduce atmospheric CO₂. The big idea is to use engineered contactors filled with chemicals to capture CO₂ from the atmosphere. [7] The high purity captured CO₂ can later be stored or used. [7] The problem is that the cost for this infrastructure is very high and the capture efficiency is too low at this point. [7] Carbon Capture and Storage (CCS) might be another method. Wilberforce et al. have suggested that the application of CCS to industrial sector might reduce CO₂ emissions by 20%. [8] They also point out that using existing oil wells to build CCS infrastructures can greatly lower the construction prices. [8] We will wait and see whether these methods can play a role in the future to help reduce CO₂ emissions.

Conclusion

The Keeling Curve is a CO₂ tracker and shows that CO₂ level is increasing every year. In order to respond to climate change and CO₂ emissions, urgent actions are needed right away. A combination of personal behaviors and technologies can help reduce CO₂ level.

© Chunchen Hong. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] M. Shiraiwa, "Facing Global Climate and Environmental Change," ACS Environ. Au 3, 121 (2023).

[2] H. Lee and J. Romero, eds., "Climate Change 2023 Synthesis Report," Intergovernmental Panel on Climate Change, 2023.

[3] C. D.Keeling, "The Concentration and Isotopic Abundances of Carbon Dioxide in the Atmosphere," Tellus 12, 200 (1960).

[4] R. F. Keeling, "Recording the Earth's Vital Signs," Science 319, 1771 (2008).

[5] J. P. Howe, "This Is Nature;This is Un-Nature: Reading the Keeling Curve," Environ. Hist. 20, 286 (2015).

[6] D. Blanco et al., "Comparison of Energy Consumption of Fluorescent vs. LED Lighting System of an Academic Building," 2018 IEEE Conf. on Technologies and Sustainability, IEEE 8671348, 11 Nov 18.

[7] N. McQueen et al., "A Review of Direct Air Capture (DAC): Scaling Up Commercial Technologies and Innovating For the Future," Prog. Energy 3, 032001 (2021).

[8] T. Wilberforce et al., "Progress in Carbon Capture Technologies," Sci. Total Environ. 761, 143203 (2021).