Encounters with the Keeling Curve

Nature

From 1969 to 1972 I was a geologist on the staff of the Hawaiian Volcano Observatory. Though our focus was an eruption of nearby Kilauea, we visited the summit of Mauna Loa once each year to make geodetic measurements as a way to monitor whether or not the volcano was inflating toward a possible eruption. During each ascent, we stayed overnight at the “Keeling laboratory” to help acclimate our bodies to the even thinner air at the summit elevation of nearly 14, 000 feet.

Thumb-tacked to the wall of our “motel” was an up-to-date hand-drafted graph of Keeling’s carbon dioxide measurements. My HVO colleagues and I had no idea that we were seeing the infancy of a graph that would eventually document incontrovertible evidence of humankind’s impact on global climate change! Charles David Keeling deserves to be smothered in credit for his experiment, though not in a CO2-rich environment!

Screen%20Shot%202019-03-29%20at%205_27_28%20PM.jpgThe Keeling Curve, 2018 edition. Credit: Wikimedia (CC BY-SA 4.0)

During the late 1950s, Charles David Keeling, a research scientist at the Scripps Institution of Oceanography, was searching for a location where he could test his newly developed technique for continuous measurement of the concentration f carbon dioxide in Earth’s atmosphere. He chose a small U.S. Weather Bureau building at an elevation of nearly 11,000 feet elevation on the north flank of Mauna Loa.

An important consideration for choosing this site was its position near the center of the Pacific Ocean, far from industrial sources of carbon dioxide. And while volcanoes themselves emit gases, he thought the possibility of contamination of the experiment with CO2 from Mauna Loa was unlikely, ephemeral, and at worst very easily identified as such and thereby deleted from the long-term record—a prediction that proved to be correct.

His measurements began in 1958. The data set continues to grow, even as I type these lines in the year 2019. What began in 1958 as an instrument test for Keeling has proved to be the source of an indisputable record that human activities are adding ever increasing amounts of the greenhouse gas carbon dioxide to the atmosphere. Long-term data collection is the key to this remarkable finding.

Three important features evident in the above graph of the Keeling data are:

During a yearly cycle, CO2 varies up and down by about 5 parts per million (ppm) due to the annual cycle of plant growth (which draws some gas out of the atmosphere) and decay (which adds it back in). Average annual atmospheric CO2 has increased from about 315 to nearly 410 ppm between 1958 and 2019. The rate of this increase has accelerated with time. If the data trend apparent by 1972 had been projected to estimate what the carbon dioxide value would be today, the result is a value of about 360 ppm rather than the actual value of about 405. If ever there was a stellar example of why long-term data collection is important, this is it.

Today, all but the most sheltered, disinterested, and perhaps totally incurious of people are aware that the climate of planet Earth is warming—that the distinction between local short-term weather events and the longer-term global weather pattern is real. A skeptic might argue that degassing volcanoes, rather than the combustion of coal and hydrocarbon fuels, are the source of the increasing amount of greenhouse gases in the atmosphere. Magma does in fact bubble off carbon dioxide and other gaseous volatile constituents to the atmosphere as this molten rock rises to increasingly lower confining pressures—as the cork is removed from the champagne bottle, so to speak.

Mauna Loa has erupted once (1984) since Keeling began his measurements there. Yet no evidence of a sudden upward spike then appears in the measured record. Yes, from year to year many volcanoes worldwide add some carbon dioxide and other greenhouse gases to Earth’s atmosphere, but in amounts far, far less than that from humankind’s continuous burning of coal and hydrocarbon fuels.

However, another unforgettable incident along my memory lane shows that carbon dioxide from a volcano can locally contaminate Earth’s atmosphere to lethal concentrations. My geologist colleague Donald Swanson and I were once potential victims of this scenario at Kilauea Volcano during our years at HVO.

Kilauea was erupting at an east-rift-zone vent named Mauna Ulu back then. Access to Mauna Ulu was by foot trail across recent lava flows. The path ascended a few hundred feet to a crater occupied by a restless lake of circulating lava. One stretch of this path crossed a low basin. During a hike to the crater, on an unusually calm day for an island famous for its nearly continuous trade winds, Don and I suddenly and simultaneously realized that we couldn’t breathe. We were in an oxygen-poor pool of air, created by carbon dioxide that had spilled from Mauna Ulu and, being a relatively heavy atmospheric gas, had settled into the low pocket for lack of a breeze. We quickly retreated. (For more details, read my 2003 book Chasing Lava.)

Ours was an easy escape from this local pool of a greenhouse gas. A broader and existential situation for Homo sapiens is whether human life on Earth can persist if we don’t greatly decrease the rate at which we add such such gases to the atmosphere—and do it very soon.

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