Early Warming. Nancy Lord

juncos rustled through the underbrush, sparrows chattered, Reger paused to pinch some soil and what might have been part of a disintegrating root. He and Berg debated the theory they were working with—that the ramparts were created during the Younger Dryas period, some twelve thousand years ago. Younger Dryas was considered to be “a cold snap” after a warming period following the last big ice age, but there was some evidence from lake sediments and peat cores that it had been a wet period here on the Kenai.

      That was the theory, but the first three radiocarbon dates they’d gotten from ramparts had dated from just fifteen hundred to five thousand years ago.

      The two men argued the theory back and forth—whether the samples were good or might have been from deep roots, what the soil profiles told them, what it might mean if the ramparts were younger than they thought. Reger was leaning now to a mid-Holocene age. “That tells us a story, too.”

      “A stranger story,” Berg said.

      “It’s not that we’re arguing,” Reger said to me. “It’s just on the table.”

      Reger was standing in a pretty big hole now. “Look what I see down here—a thin possible silt layer.” He and Berg studied the dirt, talked excitedly in technical terms, showed me—I could kind of see it—where the rampart ended and layers of overridden forest floor began. In another minute Reger was scraping, like an archaeologist, around a chunk of wood, and then a second one. Berg drew in his field notebook—the hole, the dimensions, notes on soil colors. He drew pictures of the little chunks of wood and then carefully wrapped them in aluminum foil.

      Months later, when the radiocarbon dating was completed on those chunks of wood and twelve others from the ramparts at six different refuge lakes, the “stranger story” would be told. All the samples dated within the last fifty-two hundred years, in that recent interglacial period we know as the Holocene, when climate was thought to be reasonably stable. Why would there have been such high water at that time? What might have been going on with the climate then, here in this part of Alaska and globally? Were there other data sets that could support such a finding? Lake sediment studies in the refuge have suggested that the land in question had generally cooled and become wetter over the last nine thousand years, but there was, until now, no record of such extreme wetness.

      Berg’s new theory posits that the ice-shoved ramparts associate with a large regional climate trend, perhaps involving “a series of stormy, high-precipitation anomalies that have occurred over the last 5,200 years, reflecting major changes in the North Pacific weather system.”⁷

      We ate our sandwiches, and I wandered through the woods for a while, on animal trails that followed two smaller (and presumably more recent) ramparts that lay between the one we’d dug into and the shoreline. Had I come across any of these berms in the woods on my own, I would have guessed them to be glacial moraines or eskers, features I was more familiar with. In among the birch and the sweet-smelling balsam poplar stood a few blackened tree stumps, from the fire forty years earlier. Open areas around them were filled with bursts of purple fireweed.

      I took a turn filling in the hole and then swatted more mosquitoes and listened to the far-off wavering call of a loon while Reger filled his plastic sandwich bag with lake plants to take home to his snail aquarium.

      We boated back along the east side of the lake, watching for the indentation where we would portage to the next lake and then find a trail to the road.

      I thought about the process of science—its posing of questions, all the tedious data collecting, the accumulation over time of observation, test results, reviews of results. The scientific process was slow and incremental, and conservative; it didn’t respond well to crises.

      I tried to think as a geologist might, back through time and the processes that work on landscapes. Imagine a woody plant on a forest floor, twelve thousand years ago. Or five thousand years ago. What kind of a world did either date define? Twelve thousand years ago humans were just coming across, or along the coastline of, the Bering Land Bridge, land exposed because so much water was tied up in ice caps and glaciers. Five thousand years ago our ancestors were primarily hunters and gatherers, although, at least in Asia, farming was developing on a largish scale; some clever beings invented both the wheel and systems of writing. In both those time periods the amount of carbon dioxide in the atmosphere (measured from Antarctic ice cores) was around 250-280 parts per million. Today atmospheric CO₂ exceeds 392 parts per million and is continuing to rise; levels of it and other greenhouse gases are higher than they’ve been at any time in at least eight hundred thousand years, which is as far back as ice core records go. Never in those eight hundred thousand years years did CO₂ levels increase at a rate anywhere near what we’re experiencing today. Eight hundred thousand years ago Homo sapiens was still five hundred thousand years years away from evolving; our species has never had to cope with what are, indeed, unprecedented conditions—that is, unprecedented in our human history.

      From his position in the stern, Berg talked about the Aleutian Low—that low-pressure center south of the Aleutian Islands in winter, characterized by high winds—that plays a major role in atmospheric circulation. If he and others could learn when the Kenai was particularly wet, climate modelers might be able to link that to other conditions at the time—for example the intensity of that Aleutian Low. Or to the advancement or retreat of glaciers in our part of Alaska, or to periods of intense storm activity in the Arctic. “That’s the practical way this information will be used,” Berg said. “This will help the climate modelers calibrate the models. In order to predict the future, we need to know the past. We need to run the model backward.”

      More locally, knowing something about climates of the past and conditions associated with them should inform decisions about land and water use, species conservation, and fire protection. Would it be a good thing to encourage beavers to build dams and store more water in the future? Would it be smart to reserve water for salmon streams, as opposed to using it for industrial or agricultural use? Should forest fires be allowed to burn, or should they be controlled?

      We cruised past a flock of golden-eye ducklings, all paddling furiously with no parent duck in sight. When we got over that excitement, Berg told me about other research related to “available water.” Various studies in the refuge, including analyzing photos that go back to the 1950s, have shown that wetlands are shrinking at accelerating rates. Ponds have disappeared, shrubs are filling in, and black spruces are expanding into areas that had once been too wet for them.⁸ (I see this myself. Flying over, as I do when traveling to Anchorage, I look down on the “bathtub rings” around drying ponds, as well as the new, dark growth of little spruces pushing into open areas.)

      Local meteorological records have shown a 60 percent decline in available water in the Kenai lowlands between 1968 and 2009; onethird of that, Berg has calculated, is due to higher summer temperatures and increased evapotranspiration and two-thirds due to lower annual precipitation. “That’s a big change,” Berg said. “That’s 60 percent less water to recharge groundwater, fill up lakes and rivers, and be used by plants and animals. That’s pretty dramatic.”

      With less water, areas once dominated by herbaceous plants—that is, leafy plants lacking woody stems—have been converting to shrubland at increasing rates—more than 12 percent per decade—and previously unforested areas are becoming forested at similar rates. Peat cores taken from the drying wetlands found no history of woody plant cover; that is, the sedge and sphagnum moss fens have dominated for eighteen thousand years. Only since about 1850 have those lands been drying—a drying that has greatly accelerated since 1970.

      Let me repeat that: The current invasion of Kenai wetlands with shrubs and trees is unique in the last eighteen thousand years, and it is accelerating.

      On the local level, the drying meant we were likely to see more—and more damaging—fires. Berg said, “What were fire breaks in the past are becoming fuel bridges.” A warmer climate, generally, will result in more fire activity. If the wetland areas that have acted as natural firebreaks between grasslands and forest dry out, they will no longer help control fires but will connect and speed them through the refuge and the rest of the Kenai lowlands.