CO2 Level to Reach 400, Soon Enough

The Keeling Curve


Above all else, Charles D. Keeling was fastidious with his data.

A couple of years ago, I found myself on assignment at Mauna Loa Observatory, the U.S. weather station perched just below the summit of a Hawaiian volcano. Spurred by Keeling, a longtime climate scientist at the Scripps Institution of Oceanography, this lab—still not much more than a bunch of prefab white containers sited below lava breaks—has measured the accretion of heat-trapping carbon dioxide in the atmosphere for 55 years. When Keeling began, those concentrations sat at 315 parts per million. That’s an idyllic level by today’s standards.

Indeed, as you may have heard, the CO2 monitors at Mauna Loa will soon reach—if temporarily—400 parts per million. They’ve already touched 400 ppm for at least an hour, and it’s likely that a daily average will top that level as well this month. (Stations in the Arctic touched 400 ppm last year.)

Thanks largely to human burning of fossil fuels, the planet is wrapped in greenhouse-gas levels it hasn’t experienced in the past four million years or so. Keeling’s chart has risen and risen, showing no sign of stopping; its annual average was up 2.66 ppm in 2012. Each year is a new milestone.

But as I’ve watched the incipient coverage of 400 ppm, I’ve also found myself wondering: Would Keeling, who died in 2005, be promoting this figure just yet if he were still alive? Are we all just a bit premature in this?

During my visit to Mauna Loa, woozy from the altitude, I shadowed John Barnes, the lab’s station chief, as he gave a tour to 13 Quebecois students. Whipped by the Big Island’s winds and harsh sun, we huddled in the shade of solar telescopes. With little water vapor or particles in the air, the peak of Haleakalā, Maui’s eastern volcano, was clearly visible 87 miles away. “Just the fact that you can see it tells you something about how clear the air is,” Barnes said.

We stepped into the lab’s original building, erected in 1956. Back then it took five hours to reach the lab by jeep, climbing 11,000 feet up the volcano’s pocked moonscape. (It still takes a couple of hours and a sturdy suspension.) It was a worthwhile ascent. When the sun sets, the black rocks chill and the air subsides, carrying a bit of the central Pacific atmosphere through sampling pipes and, eventually, into the lab.

As it is at nearly every remote station, space was at a premium, and we walked through a narrow hallway cluttered with abandoned equipment. Halfway down, Barnes stopped, pointing at Keeling’s wall-mounted CO2 chart, known today as the Keeling Curve.

“It’s really an amazing data set,” Barnes told the students, “because it was showing, here we are out in the middle of the Pacific, 4,000 kilometers from cities, and we’re seeing the atmosphere being affected by fossil fuels.”

Most impressive about Keeling’s work was how quickly he made his case, Barnes continued. Almost immediately, Keeling showed that global CO2 levels wane and wax each year as trees and plants in the Northern Hemisphere take in carbon to build out their leaves and stems. As that biomass decomposes, the subsequent exhalation peaks in May, making that month the CO2 record’s leading indicator.

Within five years, Keeling had definitively shown that the CO2 level was going up. It was a testament not only to how quickly human beings were dumping the gas into the atmosphere, but also to his experimental skill. (Modern scientists marvel at Keeling’s dedication, sharing his detailed instructions on, say, taking CO2 field samples in Antarctica.)

Still in the hallway, Barnes looked down at a nondescript box, packed with vacuum tubes and metal cylinders. “This is his instrument down here,” he said.

At all times, Keeling had a cylinder filled with pure nitrogen and a precisely measured amount of CO2 available, Barnes said. Every half-hour, his sampling tool would switch tasks, sniffing this reference tank, allowing a quick gauge of whether the device, which measured CO2 by how much infrared light it blocked, was drifting. The lab used the same measuring system, vacuum tubes and all, for decades, until it was well outdated, to ensure continuity in the record.

“He really got very good data,” Barnes said.

There was more on the tour: a room where the National Oceanic and Atmospheric Administration, Barnes’s employer and the lab’s owner, measures a variety of air components—CO2, methane, CFCs, even oxygen. (In parallel to CO2‘s rise, the atmosphere has had a slight drop in oxygen; not enough to worry about, though.) Barnes’s laser, which he shot into the stratosphere to probe particles. And a newer building that holds a second set of gauges, run by Scripps and by Keeling’s son, Ralph. These dueling CO2 records have corroborated one another for decades, although “ours is better,” Barnes said.

Soon enough these records will pass 400 ppm over an extended average: a week, a month, and then a year, the latter the Keeling Curve’s more standard unit of measure, given the planet’s annual exhalations. Until then it’s worth remembering: Politics and news work on the verge, but science lies in the median. I’ve kept in touch with Barnes, and, according to his best recent estimate, CO2 levels will very likely first reach a monthly average of 400 ppm in May 2014. The annual average at Mauna Loa will not hit 400 ppm until October 2015, give or take a couple of months, with the global CO2 average arriving a bit later.

Between chats this April and the last, though, Barnes has had to make one fix in those estimates. He had previously projected Mauna Loa’s annual CO2 record to hit 400 ppm in January 2016. But human CO2 emissions came too fast, as they often do, and his initial projection sagged.

In the end, he had to move the estimate up by three months.

[Graph courtesy of the Scripps Institution of Oceanography.]

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