Earth Imaging

Pictorial tributes to the natural world and to crowning achievements in science, engineering, and medicine adorn the granite walls in the cavernous lobby of the National Academies Building in Washington. On the back wall, a giant salmon hovers, midstream, just to the right of Einstein's E=mc². A much smaller fish, its design evocative of an Inuit totem, is inscribed in the middle of the salmon's body, perhaps as a tribute to native cultures or as a nod to the diminutive but central role of the human dimension in the natural world.

On a side wall, next to images of Darwin's famed Galapagos finches, is a model of carbon dioxide (CO₂) molecules—the oxygen atoms protruding from each carbon atom like the prongs of a child's jacks. Below it, a graph traces the amount of carbon dioxide in the Earth's atmosphere starting in 1958, when scientists began keeping detailed records. The curve of the graph looks like a saw blade, each tooth describing year-to-year variations in atmospheric carbon dioxide, but the upward trend in the graph is unmistakable and speaks to the reason for my visit.

Inside, I notice the names of Duke's Gabriele Hegerl and Susan Lozier printed on placards at the center tables where researchers and policy makers from top institutions around the country will soon consider the need for an early-warning system for abrupt climate change. I take a seat near the snack table where, within minutes, I've overheard the assembled experts discuss climate projections and offer play-by-play insights into Massachusetts v. the United States Environmental Protection Agency, a case before the U.S. Supreme Court to decide whether CO₂ should be federally regulated as a pollutant. (In April, the Court found that it should.)

Coastal Modeling

Hegerl, a climate diagnostician working to understand the reasons behind climate change, is a member of the National Research Council's Climate Research Committee (CRC), which has convened the panel. Lozier, a physical oceanographer, has been invited as a featured speaker because, as she eloquently explains during her remarks, when it comes to climate, "the ocean is an equal partner with the atmosphere." When she showed me her invitation to speak during our interview a few weeks earlier, Lozier mused over "abrupt"—a word that means very different things to scientists and non-scientists. Lozier tells me that when talking about climate change, abrupt means decades.

Lozier's office at Duke had been the first stop on my personal quest for more than Al Gore's "inconvenient truth." In the handful of years since I earned my graduate degree in coastal environmental management at Duke, the global climate-change story has become the best show in town—Gore even won an Oscar for his version. Did I think about global warming this much while I was at Duke? Do I think about it enough now? After all, accelerated sea-level rise and intensifying storms, both with profound consequences for our coasts, are among the most dramatic of the changes we'll see as the planet continues to warm in coming decades. How could anyone with my professional bent and my personal penchant for salty, sandy places not think about global climate all the time? With the bliss of ignorance fading into distant memory, what is a card-carrying member of humanity to do? Searching for knowledge that would help me become more than just another contributor to the problem, I headed back to the Nicholas School to catch up on the latest in climate-change science.

In comparison with the other offices I visit that day, Lozier's is a sanctuary—serene and uncluttered. Warm light from a single desk lamp casts a halo on a tidy desk. A large, well-pruned, potted succulent occupies the window alcove inside one of the towers that distinguish the Old Chemistry Building.

Lozier is explaining that the disruption of the ocean conveyor, as ocean circulation is known, could "give the signal of rapid climate change" in the form of cooler temperatures in certain parts of the world, including Western Europe.

Warm water in the form of the Gulf Stream travels north from the equator along the western margin of the Atlantic Ocean. Once past Cape Hatteras, the Gulf Stream drifts to the northeast, and the surface waters transfer heat to Western Europe, becoming cooler in the process. When they reach the North Atlantic, the surface waters—now colder, saltier, and denser—sink and flow back toward the equator in the deep ocean, a 1,000-year journey that drives ocean circulation.

As the Earth's atmosphere warms from a combination of natural cycles and human factors, ice masses around the poles are melting at accelerated rates. The fresh water being released could reduce the salinity of nearby surface waters, changing their density enough so that they wouldn't sink and drive the cycle. Lozier cites data from 2002 that show "rapid freshening" of the North Atlantic since 1965; however, her own work has not yet revealed any recent changes in the ocean conveyor. Lozier uses high-tech floats—four-foot-long glass tubes housing delicate instruments—to study currents at specific depths in the North Atlantic. After the floats spend two years underwater measuring salinity and temperature and internally recording their own location, their ballasts rupture, and they pop to the surface. They beam all of their stored measurements to a satellite. Lozier and her colleagues retrieve the data and use them to map and characterize the particular currents that carried the floats.

If the ocean conveyor were disrupted, the rapid cooling of Western Europe would be only half of the bombshell. A recent report by a scientist at the National Oceanic and Atmospheric Administration revealed that 40 percent of the CO₂ released by human activities since 1800—the same CO₂ that has been implicated as the key perpetrator in the warming of the Earth's atmosphere—has been carried by the dense, sinking waters of the North Atlantic into a reservoir in the deep sea. The disruption of ocean circulation would mean the loss of our single biggest repository, or sink, for atmospheric CO₂.

"Ninety percent of the deep waters in the Atlantic were once surface waters," Lozier explains, so we're able to monitor the penetration of CO₂ from human sources into the ocean's depths. "The time scale here is decades," she says. "We are now picking up Helium-3 and Tritium in the deep waters from the nuclear tests in the 1950s and early '60s."

In this way, the deep sea is a record, as well as a reservoir. We know from geologic evidence of deep-ocean warming that the ocean conveyor has slowed or stopped at different points in the Earth's history. We also know that at those times, the surface of the Earth looked very different from the way it does today.