By Hannah Magnuson, Dec. 20, 2018 –

Tiny bubbles of gas trapped in glacial ice are giving scientists clues about Earth’s sea level 125,000 years ago.

The gas bubbles serve as bite-sized samples of ancient atmosphere for researchers from the Scripps Institution of Oceanography at the University of California San Diego. They traveled to the ice cores of the Taylor Glacier blue ice area in East Antarctica to collect them.

The atmospheric samples give the researchers clues to understanding ocean temperature, circulation and sea level from eras long ago—clues that can help predict where today’s accelerated climate change may be taking us.

Sarah Shackleton, a sixth year Ph.D. student in the Geosciences Research Division at Scripps, explained that her research team measured the ratio of noble gas atoms present in the ice samples as an indirect way to reconstruct mean ocean temperature from the Last Interglacial, a period of warmer than average global temperature, which occurred 116,000 to 129,000 years ago.

Atmospheric noble gases like xenon and krypton are valuable to researchers because they don’t participate in biological or chemical reactions, just physics-based processes, Shackleton explained. And measuring their ratio in atmospheric samples gives the scientists predictable clues about the ratio that must have been in the ocean.

Shackleton, along with her research team, traveled to Antarctica's Taylor Glacier to collect revealing atmospheric samples.
Shackleton (back row, second from right), along with her research team who traveled to Antarctica to amass data that can feed into future climate change models. (Photo by Isaac Vimont.)

“What happens is, if the ocean cools, [xenon] becomes more soluble in ocean water so more of these gases can essentially fit into ocean water,” Shackleton explained. “And so if the ocean cools by a significant amount, that means that more of these xenon atoms can reside in the ocean, which means there are less in the atmosphere.”

Shackleton, who is mentored by Scripps geosciences professor Jeff Severinghaus, explained that oceans are a major focus of climate research because they absorb most of the excess energy that greenhouse gases trap in Earth’s atmosphere, buffering the air from more dramatic global warming.

Oceans have a very high heat capacity which allows them to take in a lot of energy without warming significantly. But the excess heat does cause ocean water to expand, raising sea levels.

The goal of Shackleton’s research is to determine how much of elevated sea level rise during the Last Interglacial period was due to ocean warming and how much was due to ice sheet loss. Though still waiting for peer review, Shackleton presented her unpublished research to fellow climate scientists in fall at the Comer Climate Conference in Wisconsin.

Shackleton’s research found that global ocean temperatures were 1-degree Celsius warmer than pre-industrial levels during the Last Interglacial period due to an ocean circulation phenomenon dubbed the “bipolar seesaw,” which refers to periods when the Northern and Southern Hemisphere temperature change is out of sync, with Antarctica warming as Greenland cools, and vice versa.

A 1-degree temperature rise should equate to about 0.7 meters (2.3 feet) of sea level rise, yet the sea levels during the Last Interglacial were a full 6 to 9 meters (19.7-29.5 feet) higher than pre-industrial levels, according to outside scientific research, mainly on fossilized coral reefs.

The rest of this elevated sea level rise must have come from Antarctica or Greenland losing significant ice mass, Shackleton explained. If researchers can determine precisely when and where this ice loss occurred, they can gain insight on where to expect ice loss in the future, as the planet continues to warm.

Shackleton's team of climate scientists set up camp in Antarctica to gather clues from a past period of warming, the Last Interglacial period. (Photo by Bernhard Bereiter.)
Shackleton’s team of climate scientists set up camp in Antarctica to gather clues from a past period of warming, the Last Interglacial. (Photo by Bernhard Bereiter.)

“When we talk about this period of time, it really comes down to the fact that sea level was higher, and we want to know—was it Greenland that lost [ice] mass? Was it West Antarctica? East Antarctica?” Shackleton said. “Because that gives us some indication of which one might be considered more unstable, or more prone to really lose mass and contribute to sea level rise.”

The Scripps research team speculates that, at the beginning of the Last Interglacial, a mass of warm water called Circumpolar Deep Water melted Antarctic ice sheets from below. Most scientists believe this process is causing the accelerating mass loss from West Antarctica today, so it’s possible it occurred during past warm periods, too, Shackleton said. To do so, the water mass, which circulates around Antarctica, would have been driven onto Antarctica’s continental shelf–the portion of the continent submerged in shallow water. Scientists think that changes in wind-driven ocean circulation could be responsible for driving the Circumpolar Deep Water onto the continental shelf.

Shackleton emphasized that her team doesn’t know for certain whether the Circumpolar Deep Water intruded onto the continental shelf during the Last Interglacial period, “But if it did, then it would be a good way to cause a lot of mass loss from Antarctica and get the sea level rise that we’re talking about from that period of time,” she said.

Her team’s data can help validate ice sheet models, which are predicting current and future sea level rise by projecting when—and how quickly—certain ice sheets will melt and how much mass and sea level rise they will add to the ocean.

By inputting sea level and climate data from the past, researchers can test the models to make sure they are realistic. Shackleton explained that her climate science colleagues are researching all aspects of past climate conditions, to inform models with a wide array of data and make future predictions more accurate.

“We’re a very small cog in a bigger wheel of trying to figure out what’s going on,” she said.

Photo at Top: Sarah Shackleton, left, and her colleague collect ice samples at Antarctica’s Taylor Glacier. (Photo by Bernhard Bereiter.)



By Hannah Magnuson, Dec. 16, 2018 –

Climate scientists veterans Richard Alley, Wally Broecker and George Denton have witnessed immense changes during their decades-spanning careers. They’re buoyed by scientific advances, but also see critical mitigation needs amid public apathy – and a policy gridlock.

Despite political stagnation, the scientists persist with pioneering research to map the way to firm predictions for what will happen to our changing climate and how it can be addressed.

Between the three of them, they have studied ice sheets and oceans around the globe in sites such as New Zealand and Antarctica, testified in front of U.S. Congressional committees, won top awards for scientific achievement and fostered the next wave of geoscientists. They convened colleagues active in research across the globe to discuss their latest findings at the annual Comer Climate Conference this fall, a climate change conference in Southeastern Wisconsin for scientists funded by the Comer Family Foundation.

Broecker, a geochemist and the longtime Newberry Professor of Geology at Columbia University, played a critical role in discovering the global ocean circulatory system. He has been studying climate change for over 60 years and is credited with coining the term “global warming” in a 1975 research paper. Alley launched the PBS series Earth: The Operators’ Manual, helped author the massive assessments of the Intergovernmental Panel on Climate Change (IPCC), and teaches geosciences at Penn State. Denton follows the tracks of past glaciers across continents and is a distinguished professor for the University of Maine’s School of Earth and Climate Sciences and Climate Change Institute.

All three men delve thousands of years into the past to better understand where human-generated climate changes may be taking us now. They study the changes Earth’s climate underwent during previous periods of warming to identify what to expect as greenhouse gases continue to heat up our planet.

On the Changing Field of Climate Change

Over the course of Alley, Broecker and Denton’s careers, climate change captured the public’s awareness and transformed into a buzzword in a polarized political landscape.

“At one point in my life I would brag that what I was doing was interesting enough that I might get a job in it and I might get a little research funding, but it wasn’t so interesting that anyone would yell at me about it,” Alley said.

Alley presented on ice fractures in Antarctica to a group of colleagues at the Comer Climate Conference.
Richard Alley calls for action in response to what the science clearly shows about climate change. (Photo courtesy of Abigail Foerstner.)

In his 41 years studying ice fields, he’s seen climate change wax and wane in the public’s interest as other issues have at times dominated the national conversation. Right now, he doesn’t think major media outlets are covering the issue enough, or in the manner it deserves, he said.

“There’s more he said, she said, they said. We jump up and down and yell at each other instead of the big discussion of ‘this is what the science says, how do we respond to that in a way that respects our values and respects our economy and our employment and our environment?’”

Despite the gridlock in the public sphere, Denton cited several significant advances within the scientific community’s study of climate change over the course of his career.

He thinks the biggest progress started with CLIMAP, a project that intertwined climate change field work with modeling. The project was first published in 1981, when numerical models were becoming more sophisticated and was run by the World Data Center for Paleoclimatology. The project’s emphasis on modeling forever altered the course of climate change research, Denton explained.

“We don’t do anything anymore without a climate model,” he said. “That was a big, big change there. It brought this sort of thing into the modern world.”

The second big advancement, according to Denton, came from developing methods to determine the absolute chronology of particles, and then testing the results through modeling runs. By using accelerators and mass spectrometers, which measure the mass of charged particles to analyze their molecular composition, the scientists can determine the ages of the particles within the ice sheets they’re studying to provide insight on glacial retreat and warming behaviors.

“Wally Broecker here was instrumental in that,” Denton said.

On the Future of Climate Change Research

Looking forward, the geoscientists anticipate large research projects and systemic policy shifts as essential measures for combating the changing climate.

Denton believes the next step for advancing climate science lies in understanding the Southern Ocean. Oceans play a crucial role in climate change, because they absorb and store much of the excess carbon emitted from greenhouse gases—resulting in ocean acidification and sea level rise.

Starting about 18 years ago, a collaborative group of researchers administered by Princeton University’s Environmental Institute distributed a series of floats all over the Southern Ocean. The floats automatically dropped to a depth that allows them to take the ocean’s measurements—a move that will enable “a new understanding of the Southern Ocean and how it affects climate,” according to Denton.

Alley advocated for the continued scientific investigation of possible climate change mitigation and adaptation efforts. “We need to know what is possible,” he said.

As an example, he cited seeding the Southern Ocean with iron—an idea discussed by researchers at the conference as a potential way to grow more plants and displace carbon dioxide so that it’s buried in the mud of the ocean’s floor. He explained that while it might help a little bit, this method might also deplete the ocean of oxygen in some areas, causing an outpouring of nitrous oxide.

Pioneering climate scientist Wally Broecker discusses his colleagues’ field research at the Comer Climate Conference. (Photo courtesy of Abigail Foerstner.)

To avoid the risk negative side effects, he predicts research will favor the implementation of a  renewable energy system.

“My gut feeling is that if we do the research and we find out the whole picture including how [climate change] would feed into human societies, then we’re going to find that it’s easier by a good bit to switch to a renewable energy system,” Alley explained.

Broecker foresees a worldwide carbon tax as a necessary measure for minimizing fossil fuel consumption. He also thinks scientists should explore geoengineering—which involves practices that directly address climate change such as removing CO2 from the air or reducing the Earth’s exposure to the sun.

“That’s our only out right now,” Broecker said, explaining that geoengineering is “a Band-Aid that [helps control] bleeding immediately but, if you take the Band-Aid back off again it’s going to start to bleed just as bad again. So that means it has to be a long-term commitment.”

On The Next Generation of Climate Scientists

 In addition to their own research, Alley, Broecker and Denton have each mentored a host of Ph.D. students and post-docs at their respective institutions. Many of their former students are now mentors themselves and expand their old teachers’ reach to countless more students.

At the Comer Conference, many scientists attending were students of Broecker or Denton, or students of their students. Together, they spanned four generations of Ph.D. scientists.

Graduate student Allie Balter was one of many scientists in attendance from the University of Maine, where Denton has long served on the faculty.

“To be able to come home [from field trips] and show [Denton] photos and hear his stories about the time he went there and what he found and his perspective and everything is really great,” Balter said.

Denton poses with a group of current and former students from the University of Maine at the Comer Climate Conference in October.
George Denton (center) posed with a group of current and former students from the University of Maine at the Comer Climate Conference in October. (Photo courtesy of Abigail Foerstner.)

“They’re our future, these pretty sharp people,” Denton said of the young scientists in attendance at the conference. He lamented the difficulty the new generation of climate scientists will have in securing funding for their research given the current federal administration that is reluctant to accept the reality of climate change.

“Many [scientists] are removing the word ‘climate’ from their proposals. They call it ‘environmental change,’” Denton explained. “It’s pretty sad.”

Broecker estimated that he’s mentored about 50 Ph.D. students and worked with about 50 post docs over the years. He explained that much of his motivation behind mentoring was “selfish enjoyment” since he loves science and had fun sharing his knowledge and forging relationships with his students.

“You can’t use your students like slaves. You’ve got to inspire them and let them go out on their own,” Broecker said. He cited his former student Jeff Severinghaus, now a professor at Scripps Institution of Oceanography  as an example:  Severinghaus decided to study California’s sand dunes for his thesis without asking for Broecker’s permission, and he went through with it.

“You have to respect that and honor it because that means you’ve got a really good student,” Broecker said. He wants his legacy to center around his love of science and fostering of new scientists, rather than on him being the “father of global warming.”

“Science is fun. Science is important. And one should be generous,” Broecker said.

Photo at top: Antarctica’s ice fields serve as research hotbeds for climate scientists studying climate changes from past eras to better understand future implications. (Photo courtesy of Jasmine Nears.)

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