After four years of conducting research in the peat bogs that cover much of the Arctic, biogeochemist Phil Camill, Bowdoin’s Rusack Professor of Environmental Studies and Earth and Oceanographic Science, and his research partners are sharing an important finding that could add another layer to the story of climate change.
It is commonly accepted that as the world warms, much of the Arctic’s frozen land, including vast stretches of peatland, will begin to thaw. In this process, not yet fully decomposed organic material—ancient shrubs, roots, grasses, mosses, etc., stored deep in frigid soil—will begin to break down.
The decomposition of this organic matter will release huge quantities of carbon dioxide into the atmosphere, hastening and worsening climate change.
“This is an unintended, unexpected release of carbon into atmosphere, a biosphere response,” said Camill, who is Bowdoin’s Rusack Professor of Environmental Studies and Earth and Oceanographic Science.
“It makes climate change potentially faster and happen to a larger degree.”
In 2011, Camill and two other scientists—David Beilman, of the University of Hawaii, and Zicheng Yu, from Lehigh University—received a National Science Foundation grant to investigate northern peatlands and their role in the global carbon cycle.
Now, after collecting and analyzing hundreds of peat and soil samples, the three scientists are suggesting an alternative climate change hypothesis, one in which certain ecosystems in the Earth’s biosphere may take up carbon and store it in a way that counteracts, in part, the soil carbon release from increased decomposition.
Understanding these processes would help us know which ecosystems are functioning this way, and the extent to which they could help avoid the worst-case warming scenario.
The vital role of peatlands
More than a third of soil carbon is stored in peatland, swampy areas made up of thousands of years worth of organic material. Around the world, peatlands encompass 4.4 million square kilometers and hold about 612 gigatons of carbon (a gigaton is equivalent to a billion metric tons). In comparison, our atmosphere today contains about 800 gigatons of carbon.
“The big daddy of peatlands is in the circum-Arctic,” Beilman said, “where the peatlands store 550 gigatons of carbon, which is why we keep an eye on this carbon pool.”
While approximately 90 percent of peatlands are found in northern regions, they do occur around the world, even in tropical zones.
The three scientists and their students collected peat cores by pulling up samples of soil up to five meters deep.
“We asked [the samples] questions: How old were you when you started sequestering carbon? How have you changed over time?” Beilman said.
Using tools such as radiocarbon dating, the scientists determined when soil ecosystems began storing carbon and at what rate. Once they did this, they observed some surprising outcomes.
Between 9,000 and 11,500 years ago, they discovered, peatlands in Alaska thrived, grew rapidly and accumulated lots of carbon. Notably, this period was marked by warmer temperatures. “Peatlands went crazy and popped up everywhere,” Yu said.
In addition, the scientists found that in the past 2,000 years, warmer, southern sites accumulated more carbon than colder, northern ones, such as in West Siberia. More recently, over the past century and a half, peat accumulation rates appear to have risen in some tundra regions.
“Plants tend to grow faster when they’re warm, when they have enough water and when they get more carbon dioxide,” Beilman explained.
As plants grow, they suck up more carbon dioxide. And the more plants there are, the more carbon they collect. Indeed, as heat-trapping carbon dioxide levels rise – as we continue burning fossil fuels – plants will be bathed in stuff they like.
The danger remains in this delicate balance that plants could get too hot and boosted respiration could reduce plant growth.
Right now, about half of all the extra carbon dioxide that humans are putting into the atmosphere is accumulating there, but the other half is being taken up by the oceans and by the terrestrial biosphere, Beilman said.
“We’ve been relying on the ocean and relying on plants and soils to take up half our carbon dioxide for the last 150 years, and we would like them to continue doing that.”
It’s possible they will, at least in some ecosystems.
“Our data suggest that the carbon sequestration rate could increase over many areas of northern peatlands in a warmer future,” contingent on peatlands remaining wet, Yu said. “A warmer planet might make peatland plants happy,” he added.
However, he cautions that these new results need to be put in context with ongoing scientific and policy work: “Peatlands won’t solve the climate problem in the next 100 years—there is simply not enough peatland area around the world to offset the rapid rate of anthropogenic carbon emission. But in the long run, over thousands of years, peatlands have the potential to be the strongest carbon sink compared to all other terrestrial ecosystems because the carbon that gets locked up there stays there for a really long time.”