On an overcast June morning Ralph Keeling unlocks the gate to the Scripps Institution of Oceanography pier and heads out onto the long concrete runway jutting over the Pacific Ocean. The sounds of traffic and other land life soon fade into the white noise of the waves and the wind. The pier was built for ocean research, but these days it is used nearly as much by scientists like Keeling, who are probing the atmosphere above it rather than the waters below.
At the tip of the pier, more than one-fifth of a mile from the shoreline, he has placed a collection of air samplers: square, funnel-like devices on tall poles that continuously draw in cool ocean air and pump it back to his lab on shore, where he analyzes the contents. For more than 20 years, Keeling has been searching for tiny changes in the patterns of the earth’s own breath, fluctuations in how the planet absorbs and emits the oxygen and carbon dioxide that make up our atmosphere.
Usually the changes are rendered in units of carbon dioxide, the greenhouse gas that typically comes to mind when we think about climate change. Indeed, Keeling’s late father, Charles David "Dave" Keeling, was the scientist credited with first proving that we are filling the atmosphere with unprecedented amounts of CO2. Dave Keeling spent decades carefully counting the CO2 molecules in the air; his long and meticulous record documented how carbon levels were rising at an alarmingly relentless rate. The graph of that rise, an incline known as the Keeling Curve, became the icon of climate change science.
Ralph Keeling, however, is tracking a different quarry. Rather than focus on carbon dioxide, he measures levels of oxygen in the air. He has found that they, too, are changing, a discovery that has helped pin down how -- and how well -- the planet is storing the carbon we generate and release. This information is vital for researchers and policymakers trying to predict how quickly CO2 concentrations in the atmosphere may rise, and what that portends for the earth’s climate.
Atmospheric measurements demand extreme precision and a certain degree of obsessiveness, yet Ralph Keeling comes across as mellow and good-natured. At 55, he still has a boyish look about him: on the day I visit his office at Scripps he’s dressed in a fleece, jeans, and Tevas, his sandy hair flopping loosely over eyes framed by large tortoiseshell glasses. He laughs easily and is patient with explanations. His office is all business -- mostly; aside from photos of his children and their artworks, the walls are covered with graphs and memos and whiteboard equations. (There are also two surfboards, which he rarely uses anymore thanks to ear troubles and an unforgiving schedule.)
An adjoining room is filled with books from his father’s library. "I never look at them," he says. "I just can’t throw them out somehow."
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Some sons agonize over whether to go into the family business, but that decision didn’t seem to trouble Ralph, Dave Keeling’s second-oldest son. The Keelings were, and remain, a close-knit family; with five children growing up in a small three-bedroom house in Del Mar, California, "we kind of had to be," says Ralph. His father was dedicated to his work but rarely brought it home. "We were more a musical home than a science-y home," he recalls. Everyone played an instrument, and evenings often turned into small-scale classical music recitals. Ralph’s proficiency on the violin earned him a spot in the New Haven Symphony Orchestra, which helped him pay his way through Yale.
From early on, it was clear Ralph shared his father’s left-brain inclination. He exhibited a mechanical bent and a knack for thinking through complex problems and arriving at elegant solutions. When his younger brother complained that he was too small to climb the big elm in the backyard, Ralph worked out a precise sequence of moves that would allow him to get himself up its branches.
In college Ralph studied chemistry and physics, although by the time he graduated, he’d also developed an interest in earth sciences. Unable to choose between graduate work in that field or in physics, he chose a program at Harvard that would allow him to study either. Even so, a year in, he still wasn’t sure what he wanted to do. He decided to join his family in Bern, Switzerland, where his father was spending a sabbatical working with researchers who were trying to extract CO2 trapped in ancient ice cores. The goal was to determine prehistoric atmospheric carbon levels and thus give much-needed context to modern-day concentrations. Ralph joined Dave in the lab.
Until then, Ralph had felt little interest in real-world experimental work. But he enjoyed "working with people and gadgets and physical objects," he says, and decided that being in a lab as part of a research team would offer a fuller, more balanced life than sitting alone in a room and playing around with theorems all day. For the first time, he felt drawn to the world of atmospheric science. He began to appreciate the beauty of exact measurements. And he finally grasped the importance of the changes his father was documenting. Even then, he says, he could sense that those atmospheric shifts portended "the end of an old age and the dawn of a new age" for the planet. He wanted to be on the front lines of that dawning. "No other field had that kind of urgency," he recalls.
Of course, his father was the very figure who had first imbued the field with that sense of urgency. Scientists had long known that burning fossil fuels caused air pollution. But there was no accurate way to measure just how much CO2 we were emitting; indeed, most scientists assumed that carbon levels varied so widely from place to place that there was no point in trying to measure them.
Dave Keeling was a young postdoc at Caltech when, in 1953, he resolved to try anyway. Unable to find any instrument suitable for the task, he decided to build one, drawing on a 1916 article that described a manometer, a machine that could precisely measure very small quantities of gas. Then he began analyzing air samples he collected in glass flasks from remote western locations, including Death Valley and peaks in the Cascades. Contrary to what the textbooks taught, he found that the amount of CO2 in the air was surprisingly uniform: everywhere he conducted his tests, the background level was about 310 parts per million. If levels really were constant around the world, Dave realized that he could use his methods and machines to track global changes in atmospheric CO2. Starting in 1958, he set up sampling stations in several places, including Hawaii’s Mauna Loa volcano. Later he would add seven more stations to create a network that covered the Pacific from pole to pole.
He very quickly made two important discoveries. First he found that CO2 levels in the Northern Hemisphere followed a distinct seasonal pattern. They fell during the spring and summer, as plants and trees grew and pulled in CO2 for photosynthesis. Then they rose in the fall and winter, as plants died or shed their leaves and released their carbon load into the atmosphere. (A similar pattern occurs south of the equator, but because there’s less land mass there, the phenomenon is more subtle.) Dave had tapped into one of nature’s fundamental cycles: the ceaseless circulation of carbon among land, air, and water.
He soon realized that humans had significantly disrupted that natural cycle through the burning of fossil fuels. Within two years of recording these atmospheric carbon levels, Dave discovered that the amount of carbon dioxide was slowly but incontrovertibly rising, by about one part per million per year. (That rate has now doubled.) When he first published his findings, in 1962, he was counting 315 carbon molecules per million. Ice-core studies would later show that preindustrial levels had hovered around 290 ppm, before shooting up in the twentieth century.
For more than five decades after that groundbreaking finding, Dave doggedly tracked CO2 levels and kept entering the data, extending the line of his graph upward. By the time he died in 2005, the count was at 380 ppm. In June 2012 it was measured at 395 ppm -- the highest level in 800,000 years.
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But the Keeling Curve tells only part of the story. As Dave Keeling himself recognized, CO2 isn’t accumulating in the atmosphere at the rate it ought to be, according to energy industry records of annual emissions. Rather, only about half of the carbon dioxide we release into the air each year stays there.
So where is the rest of it going? How much is being absorbed by the oceans? How much by plants and soil on land? Getting these answers right is of critical importance. The oceans can absorb and "lock up" carbon for as long as 1,000 years, whereas forests and other land-based carbon sinks have much smaller (meaning shorter) storage capacities. As Ralph Keeling’s Scripps colleague Jeff Severinghaus puts it bluntly, the exact whereabouts of all that unaccounted-for CO2 determine how long we can keep "soiling our own nest."
Experts refer to this as the puzzle of "the missing sink." Ralph first heard about it as a high schooler, when he and his father were talking one night at the kitchen table. At the time, Ralph could barely comprehend what Dave was saying. But some years later, as Ralph was getting ready to return to graduate school from his time in Switzerland, he remembered that conversation -- and remembered, too, his father’s idea for solving this most vexing of riddles.
One avenue worth exploring, his father had suggested, might be to measure changes in levels of atmospheric oxygen. In the air, carbon and oxygen are typically coupled in a see-sawing relationship: when the level of one goes up, the level of the other goes down. Plants on the land use photosynthesis to absorb carbon dioxide and release oxygen, for instance, while fire -- including the burning of fossil fuels -- consumes oxygen and releases carbon dioxide. In the ocean, however, the two molecules generally don’t teeter-totter in this same way; the ocean can absorb CO2 through complex chemical reactions that don’t result in a corresponding release of oxygen. Thus, Dave had hypothesized, by comparing the respective amounts of each molecule in the atmosphere, it might be possible to calculate how much carbon the land was absorbing. The remaining fraction would be the amount taken up by the ocean.
Settling back into his lab at Harvard, Ralph decided that trying to measure oxygen levels would be, as he put it, a "fun" dissertation project. Not many people would see the fun in such a formidable challenge. For one thing, oxygen is far more abundant in the atmosphere than carbon dioxide; the former makes up 21 percent of our air, whereas the latter -- for all the damage it does -- accounts for much less than one-tenth of 1 percent. Ralph would need to detect changes of just a few molecules per million, meaning he would have to make measurements that were orders of magnitude more precise than his father’s. If Dave had been forced to invent the equivalent of a dime-store magnifying glass, Ralph would need the equivalent of an electron microscope. And yet no such instrument existed.