The Earth Experiment

UM bioclimatologist tracks carbon in quest to improve climate change models

Ashley Ballantyne contends climate change has slowed during a recent “warming hiatus,” but that current models can’t predict what will happen when aggressive heating resumes.When not teaching and free from meetings, Ashley Ballantyne can be found on his computer, scrolling through carbon readings from around the globe. He searches for patterns, ones that will illuminate the carbon dioxide cycle between Earth’s surface and atmosphere.

This cycle is complex, evolving and difficult to grasp. The closer bioclimatologists like Ballantyne can get, however, the more precisely they can make predictions for a warming world.

Despite the time spent analyzing atmospheric data, or perhaps because of it, Ballantyne will be the first to tell you that while Earth’s temperatures will continue to rise with increasing CO2, just how much remains anyone’s guess. His hope is to make it as educated a guess as possible.

Ballantyne grew up near Lake Tahoe, California, which you can sometimes tell from his unkempt hair and relaxed voice. But when he explains his research, it is with focus and intensity and no small amount of gesticulation.

His career at times finds him looking back millions of years, but today he’s mostly interested in the past 15. Since roughly 1998 – about when Ballantyne graduated as a biology major from the University of California, Davis – global warming appears to have slowed down in what is commonly called the “warming hiatus.”

This slowdown is not unprecedented, Ballantyne says, and matches historical temperature data. When put on a graph, the rise in Earth’s temperature makes a stair-step pattern, the top of each step being a decade or two pause in warming similar to what we’re experiencing now.

Meanwhile, humanity continues to rapidly increase the amount of CO2 in the atmosphere. There has been no hiatus there.

This rapid rise of human-generated CO2 worries Ballantyne, who knows more than most how uncertain the consequences are for the planet. Yet he’s a scientist first and frequently refers to Earth as “a sample size of one.”

While other climatologists have published on the causes of the hiatus and skeptics have clung to it for support, Ballantyne wants to use it as an experiment. He sees a chance to examine how the carbon cycle has reacted to steadier temperatures but increasing CO2.

The Earth naturally cycles CO2 from the atmosphere into oceans and the land, and vice versa. It does so using methods ranging from plant respiration to complicated processes lasting anywhere from decades to centuries.

The land’s ability to continue absorbing carbon despite forest loss, agricultural practices and spreading cities impresses Ballantyne. “The biosphere is remarkably resilient, even though humans are taxing it,” he says.

In what he calls “a novel conclusion,” he’s finding that while the same amount of CO2 is being taken up by Earth’s biosphere, less is leaving. Plant photosynthesis has sped up, which draws carbon into the soil, but soil respiration, which expels it just like the exhalation of a human breath, has slowed down. Ballantyne says this is a result of respiration responding to the recent slowdown in warming.

But what will happen when temperatures begin to rise again? Soil respiration, like a dog panting in the heat, could begin to speed up as things get warmer. It’s a big question. As Ballantyne puts it, the Earth has been holding its breath for the past 15 years, and at some point we expect it to exhale all that CO2.

Ballantyne earned his doctorate at Duke University, where he studied iconic Lake Titicaca and its response to climate. He was based out of La Paz, Bolivia, and worked high in the Andes. He finished in 2007, the year the fourth Intergovernmental Panel on Climate Change report was published with one chapter written by Steve Running, UM Regents Professor of Ecology and Ballantyne’s future boss.

Ballantyne also was cited in the report for work he and his team did on past climate in the tropics. By measuring traces of carbon and oxygen in the growth rings of trees, they reconstructed climate and estimated temperature and precipitation from tens of thousands of years ago.

Many scientists tend to drill down, looking ever deeper into a single subject over the course of their career. Not Ballantyne. “You’re pulling on all these threads, and you never know which one’s going to lead you somewhere,” he says.

In 2012, he became an assistant professor in UM’s Department of Ecosystem and Conservation Sciences. Along with his work on the warming hiatus, he’s hired a postdoc to help him continue research on Elsmere Island off Greenland’s northwestern coast.

According to Ballantyne, 4 million years ago the island’s arctic tundra was a lush forest, home to beavers, camels and larch trees much like the modern Yukon. Its average annual temperature also was almost thirty degrees warmer than today.

“The other interesting thing about this time in Earth’s history,” Ballantyne says, “is it’s the last time that CO2 levels were 400 parts per million in the atmosphere.” In January of this year, it averaged out at 400.14 ppm, according to the National Oceanic and Atmospheric Administration.

On its website NOAA suggests “Further Reading,” and topping the list is a 2012 paper in the prestigious journal Nature by one A.P. Ballantyne.

That paper played a large role in bringing Ballantyne to Montana’s attention, says Running. He chaired the department at the time, and Ballantyne’s record of publication impressed.

“I didn’t have a paper in Nature at that age,” Running says, recalling the decision with a grin.

In that paper, Ballantyne and his fellow co-authors explored how the Earth’s natural carbon cycle is reacting to unprecedented increases in CO2.

As the paper notes, “since 1959, approximately 350 million tons of carbon have been emitted by humans to the atmosphere,” and just over half of that was then absorbed by land and sea. Despite predictions, through that 50-year period Earth continued to absorb CO2 from the atmosphere. Far from slowing, the amount of CO2 being taken into oceans and the land has increased.

Focused on the natural carbon cycle, this was like his current work on the warming hiatus, but the scale of time was much longer, and the findings less specified as a result.

“As a human I’m terrified of what’s happening,” he says, “but as a scientist, I think it’s a pretty cool experiment.” He laughs and adds: “And it’s a pretty challenging problem to work on, and a very worthy one.”

For now Ballantyne sticks to the science, and has not taken an advocacy role, though he feels certain that humanity needs to move past fossil fuels. He believes that you need credibility and accomplishment as a scientist before you can consider speaking as an advocate.

Running, who often does take an advocacy role, agrees that it’s better to build credentials as a scientist than speak out as a citizen too early.

“Hopefully 10 years from now he can,” says Running, “and he’s on a good start.”

— By Andrew Graham

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