What Ancient Rocks Can Tell Us About the Effects of Global Warming

Excerpted from 'Deep Water', a TED Book by Daniel Grossman.

In 2009 my friend Maureen Raymo, then a professor at Boston University, invited me to join her geology expedition to Australia. At first, the trip's purpose seemed arcane to me: Raymo would study sea level during the geologic period called the Pliocene. I knew little about the Pliocene then, except its duration: from 5.3 to 2.6 million years ago. I flew to Melbourne. During the following month of work and travel, Raymo would tutor me in her studies. Later Raymo and I received a grant to work together and I made some videos about her research. Raymo, who has high, wide cheekbones, jet-black hair and a steady, soft-spoken presence, would be a stabilizing force among her crew.

Through Raymo, I met Paul Hearty, a geologist who'd joined her to perform the critical task of identifying Pliocene Age sea-level rocks. By looking at the rocks on past shorelines, Raymo and Hearty hope to learn more about the correlation between average planetary temperature and sea level. Before long, Hearty, talented and cantankerous, had me both exasperated and amazed. He showed me ways that scientists are achieving better predictions of future sea-level rise -- and gauging whether the increase will be merely very bad or absolutely catastrophic. As I followed Hearty's work over the next three years, I'd find his conclusions compelling and important at first, but later, of some, I'd be dubious.

When I arrived in Melbourne, Hearty, Raymo and two other colleagues -- Hearty's disciple and former graduate student, Michael O'Leary, and Marci Robinson, a paleontologist from the USGS -- were already preparing for our expedition. They'd rented two vehicles for the 4,000-mile research road trip: a battered white van jacked almost two feet off the ground and set up for sleeping two, and a Winnebago-style camper. In addition, they'd rented the sort of super-precise GPS that mineral surveyors use, nearly 100 times more accurate than the typical Garmin in your car.

The day of our departure didn't begin well for Hearty. A clasp had ripped off his favorite clogs. A screw in his glasses had fallen out. His hasty repair -- a safety pin in a hinge of his shades -- gave him an incongruously punk look. The expedition overall had also suffered a series of small setbacks and delays, provoking Hearty's impatience and ire. A red warning bulb on the camper's dashboard had flickered on, indicating a transmission leak. The rental agency replaced the vehicle. But further troubles soon arose. The new camper was worse than its predecessor. Its hand brake -- critical on the rough terrain we'd traverse -- didn't work. Its battery wouldn't hold a charge.

We returned to the rental agency, where Raymo calmly presented our paperwork. A harried attendant searched for yet another replacement. But the season for outback travel was in full swing, and no vehicle with sleeping berths was available. We reluctantly accepted the best alternative on the lot, a silver SUV. The clerk, fielding calls, settling bills and fixing problems, sighed and said, "I haven't had a chance to scratch my nuts." Meanwhile, between errands, we caught some breakfast at an Italian café. In the middle of the meal, Hearty, impatient, blurted: "Let's get out and start putting rocks in bags!"

Hearty's eyes are light bluish-gray and set deep. When he's agitated, his brows bunch into furrows reminiscent of the crevasses of glaciers he once studied. For thirty years he's labored to prove that if Earth warms just a couple degrees, as many scientists forecast, the huge glaciers in Greenland and Antarctica could substantially melt in mere decades. He has based his predictions on his studies of two recent (geologically speaking) warm spells that occurred about 125,000 and 400,000 years ago. They're called Stages 5e and 11, respectively. Hearty had concluded that sea level had risen about 20 meters (62 feet) during the earlier of these heat bouts -- higher than almost anyone else had yet determined.

If Hearty is right, his conclusion has grim implications for our own future.

At the time of our trip, Raymo harbored questions about Hearty's results. His thinking on the subject was at odds with that of most other researchers. Still, Raymo's reservations did not change her high regard for the man. She'd asked him to join the team for a separate reason, about which she possessed no qualms: Hearty seems to possess a clairvoyant ability to envision the moment in the past when the million-year-old rock was formed. Raymo had earned her scientific kudos analyzing gummy seafloor sediment. She rarely handled limestone and sandstone -- hard rocks -- like those she'd collect in Australia. She'd once owned a rock hammer, but had long since lost it. Hearty, on the other hand, had blistered his palms for decades cracking open such rocks. He reads rock. His real eyes might see scrub-covered limestone and fossilized coral, miles from any current shoreline. But his mind's eye sees surf and spray and dunes. In the field, Hearty stares at rocks, sometimes from several angles. He tastes them with the tip of his tongue. He strikes them with his hammer and listens to the pings.

Raymo calls him, with affection, the Rock Whisperer. I've read many of Hearty's 100 or so scientific papers. I've chatted with him and his colleagues for hours, educating myself, cross-checking details. My inquiries at first convinced me that Hearty's gloomy predictions about sea-level rise might be important, and overlooked for the wrong reasons. For a while, I suspected that Hearty had gotten a raw deal, that his sometimes alienating demeanor, and his absence from collegial conferences and workshops, might have cost his ideas fair hearings.

Can ancient rocks really tell us just how fast and how much polar ice will melt? Hearty believes they can, unequivocally. And such predictions matter tremendously. James Hansen, the most prominent scientist urging the United States to act quickly on the threat of climate change, says extra warmth might transform Earth into "a different planet." By "different," he does not mean better. Ecosystems, weather and areas of human habitability will completely reshuffle. Cities, towns and agricultural areas could be destroyed, and populations displaced. But the most important consequence of this radical warming might be glacial melting and subsequent sea-level rise, says Hansen, who directs NASA's Goddard Institute of Space Studies.

Read the entire ebook 'Deep Water' here.

Learn more about Daniel Grossman and his work here.