In the late 1950s, a scientist named Charles Keeling placed instruments designed to monitor the amount of carbon dioxide in the atmosphere at research sites that were chosen for the relative cleanness of their air. The first was on the summit of Mauna Loa in Hawaii, and the second was in Antarctica. As the fifties segued into the sixties, two patterns emerged from the resulting data. The first is the natural annual cycle. Carbon dioxide levels in the atmosphere peak every May. As spring advances in the Northern Hemisphere, the global increase in photosynthesis (due to the fact that the Northern Hemisphere holds most of the world’s land) starts to remove carbon dioxide from the air, and global CO2 levels go down. But in the Northern Hemisphere autumn, when the leaves fall, decay, and release their stored carbon, the CO2 levels start to go back up. The second pattern Keeling observed was the steadily increasing trend in CO2 amounts on a year-to-year basis. Keeling’s data were clear enough by 1965 that the increase in CO2 and its implications for global temperatures were mentioned in a broad report of the effects of air pollution presented to President Lyndon Johnson by his Science Advisory Committee. Frank Ikard, president of The American Petroleum Institute, would bring the issue to the attention of the Institute’s members in its annual meeting the following month. “The substance of the report is that there is still time to save the world’s peoples from the catastrophic consequence of pollution,” Ikard said, “but time is running out. One of the most important predictions of the report is that carbon dioxide is being added to the Earth’s atmosphere by the burning of coal, oil, and natural gas at such a rate that by the year 2000 the heat balance will be so modified as possibly to cause marked changes in climate beyond local or even national efforts.”
Figure 1
Ikard drew that conclusion based on a relatively small amount of data, but as Figure 1 shows, concerns about the trend in atmospheric amounts of carbon dioxide (along with their subsequent effect on climate) proved to be very well-founded. In 1960, the Mauna Loa device recorded 320 parts per million (ppm) of carbon dioxide in the atmosphere for the first time. (Basically, if a slice of the atmosphere could be broken into one million equally sized cubes, carbon dioxide would fill up 320 of those cubes.) In 2013, the site recorded 400 ppm for the first time. And this May, it recorded 420 ppm for the first time.
So yes, carbon dioxide levels have increased by a lot over sixty years. But has the rate of increase slowed down, at least? And has the global drop in emissions that resulted from the pandemic noticeably affected this rate? To answer this question, we are going to look at the Keeling curve in another way. Figure 2 shows the change in the measured monthly mean of CO2 measured at Mauna Loa relative to the previous year’s amount for the same month. The first thing that sticks out is the general increasing trend; this means that the rate of increase has, for the most part, accelerated. But the curve is not a smooth one, and both natural and artificial events emerge from the data if you know what to look for. Note the large spikes in 1998 and 2016. These coincided with major El Niño events, and there is a physical explanation for that correlation. There was also a prolonged period in the late 1980s and early 1990s where the rate of increase steadily dropped, although it did not disappear. This coincided with the collapse of the Soviet Union and the Eastern bloc. As for the past year, the rate of increase is a bit low relative to recent years. This can be easily explained by the pandemic, but it is worth noting that atmospheric levels of carbon dioxide still increased at a rate that would have been considered high in the decade of the 2000s.
At this point, you might be wondering why events which produce a noticeable drop in emissions do not decrease the amount of carbon dioxide in the air. The primary answer is that carbon dioxide, once put in the air, can hang around for a very long time. To be specific, it has a half-life in the air of about fifty years. So roughly half of the CO2 emitted in 1971 years ago is still in the air, and half of the emissions caused by the electricity and transportation we use today — unless a cost-effective means of direct removal is developed in the meantime — will still be there in 2071. This means that it will take a prolonged, substantial reduction in emissions before we can slow down, and ultimately reverse, the increase of CO2 in our atmosphere.
There is another factor to consider as well. The permafrost, or tundra, stores carbon dioxide in the ground for very long periods of time. But when the permafrost starts melting due to rising temperatures, the carbon dioxide gets released back to the air. This is an example of a positive feedback, where warming creates an effect that leads to more warming. So the warmer we allow the temperature to reach, the harder it will be for nature to bring carbon dioxide levels back down near pre-Industrial levels should we ever stop emitting CO2.
We are therefore still a long way from getting atmospheric amounts of CO2 under control. While there is grounds for optimism regarding the cost of transitioning to clean sources of energy, the transition needs to be implemented with much greater urgency. A major climate conference is happening in Glasgow, Scotland beginning on October 31. Emissions reductions will be discussed. Whether the discussion will lead to serious action remains to be seen.
