U.S. Geological Survey
Scientists are reconstructing Earth’s climate history to understand what past changes reveal about the present and future.
Scientists nail down past climate to show high stakes of warming
by Gretchen Roeckerand Megan Taylor Morrison
Oct 12, 2011
Gretchen Roecker/MEDILL
Geochemist Irene Schimmelpfennig, of Columbia'sLamont-Doherty Earth Observatory, is a glacial sleuth. She calculates times when ice advances and retreats in the shrinking Swiss alpine glaciers bymeasuring the concentration of isotopes in rocky deposits.
Megan Morrison/MEDILL
The trusted triad: Richard Alley, Wallace Broecker and George Denton. The three scientists carry on the late Gary Comer's philanthropic mission to seed ground-breaking climate research and organize the Comer Conference to share the findings each year.
Gretchen Roecker/MEDILL
To provide a space for scientists from around the world to present and display their research at the Comer Conference, an airplane hangar is transformed with tarps and tables.
Outside the hills are green and forested, but inside the talks focus on the climate science underpinning the double threat of drought and rising seas, already resulting from global warming.
Thirty-three scientists gathered at the recent annual Comer Conference on abrupt climate change to share a year’s worth of research from across the globe. They sit at tables, chatting congenially.
In the front of the room, a wiry man with glasses and a beard stands and raises a small device to a microphone.
Moooooo.
In the spirit of camaraderie at the conference, the quirky cow call announces the beginning of the meeting and tells researchers when the time for their presentations is running low.
The man with the microphone introduces himself as Richard Alley, a geoscientist from Pennsylvania State University and a force field of energy. His noisemaker is a gift from Columbia University’s Wallace Broecker, the 80-year-old titan of climate change research who coined the term“global warming” in the 1970s.
“We have to get the science nailed on abrupt climate change,” Alley says, driving the last three words home with full-body, staccato accents. Things that happen so fast “really matter to people in the real world.”
It’s imperative “to tell people honestly and realistically what is happening and why it matters,” he adds.
In geologic terms, “abrupt” can describe changes that take place over centuries or millennia. But some of those shifts happen quickly– and all of them matter because they can help predict how humans are driving climate changes at a rapidly accelerating pace.
“In the next two days, we’re going to see what we learned,” Alley says.
Alley warmly welcomes the scientists, acknowledging Broecker and George Denton, a renowned climate scientist at the University of Maine. The three became close friends and advisers to Chicago philanthropist Gary Comer as he funded abrupt climate change research.
Since Comer’s death in 2006, they have continued to identify promising research for funding and to coordinate the meeting hosted by his children, Stephanie and Guy, at their family retreat. Together, they carry on a legacy that has committed some $50 million to climate change research projects and facilities since 2002.
Over the last year, with help from the Comer Science and Education Foundation, scientists at the conference have studied ice, rocks and lakes from Asia to Argentina. By filling in missing pieces in the puzzle of the planet’s past, they are painting a robust picture of climate change and its predicted impacts on global warming.
A modern perspective
Research this past year focused on what drives rises and falls in temperature, glacier size, and precipitation rates during the Holocene, the current geologic period that began with the end of the last ice age 12,000 years ago. Scientists compare past patterns of this relatively stable period to better understand today’s unprecedented warming trends.
Understanding past data can help society prepare to “make a contiguous plan” for future changes, said Jorge Strelin, a staff geologist with the Antarctic Institute of Argentina.
“This area of science... is a very important topic to be considered at present because of climate change,” Strelin said. “We should be prepared to participate in climate change and to understand what will happen in the future.”
Although changes in temperature have occurred naturally over earth’s history, Denton said research reveals that current conditions no longer follow past trends.
“Under normal circumstances, the earth would be slipping back into an ice age,” Denton said. “Of course, the conditions aren’t natural now because humans are pumping CO2 into the atmosphere.”
Carbon dioxide, or CO2, collects the air as by-product of burning fossil fuels. As it accumulates in the atmosphere, CO2 and other “greenhouse gases” form an invisible heat blanket, trapping thermal energy that would normally escape into space.
The scientists gathered at the conference have looked closely at other potential causes for aberrant temperature patterns, such as ocean currents, sunlight and volcanic ash. Carbon dioxide, they believe, is the key factor and is rising at unprecedented levels due to human use of fossil fuel.
Clues to climate patterns
In order to understand Earth’s recent climate history, these scientists collect and analyze materials from almost every continent. They find clues to past climate in tree rings, insects, cosmic ray isotopes, mile-long ice cores, lakebeds and caves. Tapping into this evidence, they calculate the past temperatures and chemical compositions on earth.
“One of the general questions is always if climate changes are just regional or hemispheric or global,” said Irene Schimmelpfennig, a geochemist at Columbia’s Lamont-Doherty Earth Observatory. “If you have the same signals in very different parts”of the globe, ”that shows that there’s a link.”
For Schimmelpfennig and others studying glaciers, determining the age of moraines, the rock formations deposited as glaciers advance and exposed when they retreat, helps fill in a chronology of how a glacier has grown or shrunk in response to “climate forcings”like carbon dioxide and solar radiation.
“What we can conclude from our reconstructions is that based on small climate changes glaciers fluctuated heavily,” Schimmelpfennig said, adding that the speed of the current glacial retreat seems to be unprecedented. “If the warming goes on like this, glaciers may disappear in a few years” in some parts of the world.
Joerg Schaefer, who heads the cosmogenic dating group at Lamont, refers to glaciers as “climate recorders” because of their sensitivity to shifts in temperature and ability to freeze data about climate conditions.
“Whenever a glacier is changing, it’s dramatic for the environment,” Schaefer said. “Whatever will happen in the near future will have dramatic impacts on the landscapes and the people living there.”
Dating glacial sediments
Along with Schimmelpfennig and other scientists and students, Schaefer has helped refine a popular new method used to calculate the timing of glacier growth and retreat: beryllium-10 surface exposure dating.
Beryillium-10 is an isotope formed when cosmic rays hit Earth’s surface. As a glacier retreats, cosmic rays react with oxygen, silicon and other elements in the uncovered rock to produce Be-10. The longer the rock is exposed, the more Be-10 accumulates. Scientists such as Schaefer and Schimmelpfennig use the concentration of Be-10 atoms to calculate the age at which the rock was exposed.
In the last year, Schaefer said, Be-10 dating has become much more precise as researchers have refined data on how quickly the isotope builds up naturally.
“That’s a real game-changer,” Schaefer said, because the recent progress gives scientists the key to glacier moraines, an almost untapped but near-global climate archive. “It really connects the paleo-record to present day, and it gives a continuous baseline against which you can calibrate the ongoing climate change.”
Backed by a more precise method, Schimmelpfennig, Schaefer and others have been able to show links between abrupt climate changes identified in Greenland and the Swiss Alps, such as the retreat of the last ice age glaciers at the beginning of the Holocene period.
Hydrology across history
While some scientists are exploring climate markers in glaciers at the poles and in New Zealand, Patagonia and Europe, others are investigating how water systems, temperature and climate intertwine by studying past and present shifts in Earth's hydrology.
“A major result of the temperature change is a shift of rain belts and water supplies,” Denton said. “That’s the major message coming out of the paleoclimate changes, both for the ice age and for the Holocene.”
As the hemispheres heat or cool, the location of the highest mean temperatures moves north or south and pulls the rain belt with it, Denton said. This is the Earth’s thermal equator, and the shifts in it can cause lakes to turn into deserts and vice versa.
Aaron Putnam, a geochemist at the Lamont-Doherty Earth Observatory, and several of his colleagues who have received Comer funding, saw that shift first hand in Asia. The scientists sifted through clues revealing that a desert in western China was once a vast lake that dried out at the same time as the once-wet western United States.
Similar mid-latitude drying events could occur again as CO2-driven temperature rise transforms rain systems.
“The northern hemisphere, because of its huge landmass, will warm more quickly than the southern hemisphere and more dramatically,” Denton said. The resulting changes in distribution and intensity of rainfall could worsen monsoons and cause severe drought.
“Potentially, we are messing with some big forces,” Denton said.
At the end of the last ice age, a dramatic northward shift of the thermal equator happened “in something like 50 years,” Broecker said.
As global warming continues the thermal equator, which marks the highest average yearly temperatures around the world, could quickly slide north again, altering water patterns around the planet.
Warming is currently causing measurable changes in water distribution south of Putnam’s parched desert.
Adam Hudson, a University of Arizona geosciences graduate student, said he was eager to show the researchers his preliminary findings that the Tibetan Plateau region in Central Asia is rapidly getting wetter: in the last 30 years, the total lake area on the plateau has grown by up to 35 percent, likely because of melting permafrost.
"I've been thinking about this for about three weeks or so," Hudson said of the fresh observations. "I was so excited about it I decided to present what I had so far."
Excitement about sharing research and getting feedback from peers spilled from official sessions into the outdoor dining tent over plates piled high with fresh tomato salads and sweet cornbread. Adi Torfstein, a geochemist from Lamont, said coming to the Comer Conference gives him a chance to talk to peers in an atmosphere he doesn’t find at larger science gatherings.
"There’s a lot of opportunity to interact and to talk to really essential people," Torfstein said. "The big meetings are more industrial. That’s the magic of this conference -- the proximity.”
Torfstein is studying the "dust archive" in ancient Dead Sea sediments to better understand the history of environmental conditions related to hydrology and dust storm frequency in the Middle East, where changes in water availability could severely impact agriculture and heighten political tensions.
"This area has its share of geopolitical problems," Torfstein said, "and water scarcity, which is expected to be more severe in the near future, can only add to these problems."
Melting ice, rising trends
As emcee Alley zipped through a colorful presentation on "Some Ice Stuff,”showing that paleoclimate research isn't just about tracing the past, but about extending that sketch and its implications through the present and into the future. Studies of how vast swaths of ice and water have responded to temperature shifts in the past indicate that a warmer climate could mean meters of sea level rise above current coastlines.
"The trend in sea level is clearly up," Alley said, noting that warmer temperatures are causing sea water to expand and increasing glacial melt.
In the last century, average temperatures have risen by 1.5 degrees F and estimates for future temperature rise from CO2 and other fossil fuel emissions range from about 3 to 15 degrees. The temperature rise could potentially have huge impacts for earth, Alley said.
Greenland's massive ice sheet, which is rapidly melting and dumping icebergs into the North Atlantic, could contribute to projected sea level rise of about one meter, Alley said. While Greenland’s ice is unlikely to slip suddenly into its salty surroundings, Alley said, the fate of glaciers at the opposite pole is far less certain.
Thwaites Glacier, on the West Antarctic Ice Sheet, may be poised to slide off its current perch. If it doesn't stabilize on another "bump" in the sea floor, Alley said, Thwaites could lead to the collapse of the ice sheet and a relatively rapid three-meter increase ocean levels.
"We don't really know how fast it could go," Alley said, cautioning that the physics of two-mile high ice cliffs isn't yet well understood. "If the world's going to do something that makes that meter of sea level rise this century too small, this is probably the place" where "there really could be an abrupt climate change."
Studying the past, working for the future
Despite the uncertainties and challenges in understanding abrupt climate changes ancient and new, the scientists agreed that the support from the Comer Foundation and their globetrotting leaders and peers has helped accelerate vital work. Both the funding and the collaborative atmosphere of the conference assist their efforts.
“It was Gary’s idea not only to help fund research, but to make sure the people who were doing it got together in a congenial way,” Broecker said. “We’ve worked hard to try to use the money that he put aside for us in a wise way, and also to make sure these meetings were fun for everybody and intellectually stimulating.”
Comer began offering fellowships for climate researchers through the Comer Science and Education Foundation in 2004, three years after A relatively ice-free voyage through the historically ice-choked Northwest Passage spurred his interest in Earth’s changing climate. The foundation continues to provide young scientists with the funding needed to launch seminal research.
The scientists agree that Comer’s funding has allowed them to gather data at an unprecedented rate.
"Gary Comer probably generated 20 years of research in the course of five," Putnam said.
The ability to push research frontiers and share results sheds a hopeful light on an uncertain future, Alley said.
"We're doing good science the right way,” Alley said. “Getting it into the public eye is not just fun, it really is how our civilization works. We’re a little piece of that.”
