Charles David Keeling

There is a curve so beautiful to the mathematician that it set me off on this whole adventure of the study of climate change: it's called the Keeling curve, or the Keeling Data, in tribute to the man who began collecting it, and here it is:

What makes it beautiful?

1. In contrast to so much real-world data, this data appears to be on a mission. It's so regular! Usually real-world data is tremendously noisy, flailing around, and you have a devil of a time figuring out what it's doing, what's behind its appearance. But no such problem with this data set.

2. On a similar note, we can see clearly two distinctly different kinds of steady behavior. If it were your retirement portfolio, you'd no doubt regret the sawtoothing up and down, but you'd be cheering the steady rise in "value". You might puzzle over that sawtooth shape to the graph, but, knowing as you do the seasonal behavior of markets, you'd probably be able to write it off, especially given the general upward trend.

3. Finally, the curve rise is accelerating (as James Hansen will mention below): it's not just trending upwards as a straight line, but rather growing higher ever faster. I use it routinely in my courses to teach students that "linear regression may not be the right tool for your data." So often modellers reach for the tool of linear regression, whether appropriate or not, and then report their conclusions based on it -- whether appropriate or not. So, as a mathematician, it serves a very useful purpose.

(from Keeling's autobiographical Rewards and Penalties of Monitoring the Earth )

The data itself has been called "...the most important envirionmental data set taken in the 20th century", and I agree. It tells a very important story, one which begins with Charles David Keeling (American, 1928-2005).

Keeling was a young researcher in the late 1950s, and he felt that it was important to see what was happening to Earth's atmosphere. Was the carbon dioxide level actually building up because of human activity, or was the ocean absorbing all that carbon that humans were throwing up into the air? That was his question, and it turned out that the answer (and the data he collected) would make him famous.

Well, not rockstar-famous -- but, you know, famous among scientists. That probably seems like a pretty lame form of famousness....

It's not just that he collected important information, but that he collected it so well: "Charles David Keeling was a stickler for precision. The measurements of CO₂ he began in the 1950s were an order of magnitude more accurate than previous measurements. In recognizing the value of a continuous record, and obtaining it, he brought a clarity to the problem that altered our perceptions about global change and the degree to which the Earth can absorb the human assault." -- Dr. James Hansen, in his Is There Still Time to Avoid `Dangerous Anthropogenic Interference' with Global Climate?: A Tribute to Charles David Keeling.

Keeling began his work at Caltech, in Pasadena, CA, in the early 1950s. He got hooked upon constructing a sensitive device for measuring atmospheric CO₂ (a precision gas manometer), and soon he was taking readings up and down the west coast of the U.S. He discovered a day/night variation, which he was able to attribute to plant respiration and soils shedding CO₂ differentially during the day. CO₂ levels were about 310 ppm. In 1956 Keeling proposed a global program in atmospheric CO2 concentration at different sites around the world, including the South Pole and at Mauna Loa, in Hawaii. The program received funding, through the end of 1958. The first observation at Mauna Loa had a reading of 313 ppm. He was surprised to see it rise steadily, however, to a maximum in May, followed by an equally steady decline into October. Keeling realized later what he was seeing: "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." As Keeling continued monitoring CO₂, he found that the cyclical pattern repeated, and that the yearly trend was a steady increase in CO₂ level. These were two extraordinarily important observations.

Perhaps more importantly, the curve became a lightening rod for those who felt that anthropogenic climate change was a threat, and helped garner attention scientifically and in the public. It continues to play that role, and, as Hansen noted in his tribute to Charles David Keeling, "...first a few details about CO₂. This Keeling curve may look almost like a linear increase. It is not. CO₂ growth is closely related to fossil fuel use. We know two numbers accurately in the CO₂ story. One number is the annual global CO₂ increase, which we know for half a century, thanks to this record started by Dave Keeling. The second number is the global annual emissions of CO₂ from burning of fossil fuels."

And it turns out, not surprisingly, that the two are very strongly correlated. It seems that about 57% of the CO₂ burned ends up in the atmospheric record of Keeling.

Today we can watch 800,000 years of change in the CO₂ record. But the tail end of that history, and perhaps the most important 50-some-odd years of that, is thanks almost entirely to Charles David Keeling, a climate hero.

• The Keeling Data (continually updated to the most recently available)

• The Keeling Curve (maintained by Scripps), and its history (from which I borrowed liberally for this vignette -- thanks!).

• Trends in Atmospheric Carbon Dioxide, from NOAA.

  There is a marvelous movie of 800,000 years of CO₂ in our atmosphere on the site.

  If you check out the graphs, notice that in spite of the Kyoto Protocol (1997), a treaty with the stated purpose of reducing greenhouse gas emissions, the planet has shown no evidence of a slow-down in CO$_2$ pollution. In fact, it appears from the graph that the trend is actually accelerating.

• Keeling wrote a great autobiographical piece, in which he bemoaned our abuse of the planet. Many great quotes, including this one: Writing in 1998, Keeling said that "... a more prudent attitude would be to heed the rise in atmospheric CO₂ concentration as serious unless proven to be benign. If scientists would make clear to the public the wisdom of this cautious approach, people would demand to be better informed about what scientists already know. The collective talent and wisdom of a species self-named Homo sapiens might then be better directed toward the issue of global warming."

  Keeling further observed that "[i]t has been over 40 years since Roger Revelle and Hans Suess (56) pointed out that the burning of fossil fuels was a large-scale geophysical experiment that 'if adequately documented may yield a far-reaching insight into the processes determining weather and climate.' There was no sense of peril then, just a keen interest in gaining knowledge. Now, four decades later, there is a hint, perhaps more than a hint, of peril. Nevertheless, and despite the heightened political awareness of the greenhouse problem indicated by the Kyoto meeting last winter, most governments have shown little heightened interest in environmental monitoring."

  What is our "peril level" today?