Drying of northern wetlands has led to much more severe peatland wildfires and nine times as much carbon released into the atmosphere, according to new research.
The most dangerous amplifying carbon-cycle feedback we face in the near term is, I believe, the thawing northern tundra. It is poised to turn the Arctic from a carbon sink to source in the 2020s, releasing 100 billion tons of carbon by 2100, according to a 2011 study.
That study found, conservatively, that carbon emissions from a thawing permafrost are “strong enough to cancel 42-88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible” and accounting for it “will require larger reductions in fossil fuel emissions to reach a [given] target atmospheric CO2 concentration.“
But there are a host of other very serious amplifying feedbacks — or vicious circles — whereby an initial warming leads to changes that cause more emissions, which in turn lead to more warming (see partial list at end). One of those involves the drying of the peatlands.
Most of the world’s wetlands are peat, which are better known as bogs, moors, mires, and swamp forests. Wikipedia notes, “Under the proper conditions, peat is the earliest stage in the formation of coal.” Here’s why peatlands contain so much carbon:
Peat is the accumulation of partially decayed vegetation in very wet places and it covers about two percent of global land mass. Peatlands store large amounts of carbon owing to the low rates of carbon breakdown in cold, waterlogged soils.
A 2008 Nature Geoscience study — “High sensitivity of peat decomposition to climate change through water-table feedback” — projects that “a warming of 4°C causes a 40% loss of soil organic carbon from the shallow peat and 86% from the deep peat” of Northern peatlands. And that amplifying carbon cycle feedback is dangerous for three reasons:
- The northern peatlands are believed to store some 320 (+/- 140) billion metric tons of carbon, roughly half of what the atmosphere contains.
- Peatlands tend to emit much of their carbon in the form of methane, which is more than 20 times as powerful a greenhouse gas as carbon dioxide (and 100 times more powerful over a 20-year period).
- A warming of 4°C this century is all but inevitable if we don’t sharply reverse emissions trends quickly (see “An Illustrated Guide to the Science of Global Warming Impacts“).
Now, a new study does some experiments and makes some observations to look at the impact of drying on peatlands. A coauthor sums it up:
“Currently, peatlands are considered important global stores for carbon. But we’ve shown that human disturbance or climate-induced drying can switch peatlands from sinks to potentially huge sources of carbon, with losses associated with severe burning far outweighing long-term rates of sequestration.”
“Russia, Indonesia and Canada all have abundant peatlands, but they also have been hotspots for intense peat fires in the past decade,” said Guelph professor Merritt Turetsky, who worked on the study with William Donahue of the Water Matters Society of Alberta and Brian Benscoter from Florida Atlantic University.
In pristine states, peatlands often resist fire because of their wet soils. “Our study shows that when disturbance lowers the water table, that resistance disappears and peat becomes very flammable and vulnerable to deep burning,” she said.
Recently, destructive peat fires plagued the Moscow region. In the late 1990s, severe Indonesian fires in drained peatlands released carbon equivalent to 40 per cent of annual global fossil fuel emissions.
I discussed the research on Indonesia peatlands here: “For Peat’s Sake, Stop the Palm Oil Madness.”
Peatlands store vast amounts of carbon by pulling carbon dioxide out of the atmosphere. For millennia, they’ve accumulated plant debris — the remains of wood, moss, and other plants — and locked it up in layers of saturated peat more than five metres deep in places.
Northern peat covers large swaths of the landscape. Because about half of that peat consists of carbon, it is a globally important carbon pool.
But peatlands are also carbon sources, as this same debris fuels wildfires. “While fire is a widely recognized disturbance in upland forests, the impacts of fire on peatlands and their carbon storage have been largely overlooked,” said Benscoter.
The majority of the world’s peatlands are located in northern regions, and Canada is home to some of the largest on the planet….
Previous studies have documented the effects of land use practices and global warming on the ecology of peatlands. “But we wanted to examine how decades of lowered water table in peatlands might affect wildfire behaviour, and that required a very large experiment.”
To determine those effects, the researchers used a unique outdoor laboratory. A large section of a boreal fen near Slave Lake, Alta., had been drained over 20 years ago in a wetland drainage project. A portion of the fen including drained and pristine plots burned in a wildfire in 2001 allowed for a natural experiment.
Earlier research had documented increases in tree growth and carbon storage after drainage. “But nobody had looked at the impacts of dewatering on fire intensity and associated carbon gains or losses,” Donohue said.
The results were surprising, he said. Long-term drainage actually increased tree productivity and carbon storage in the fen soils. But the lower water table also changed wildfire conditions, and losses of soil carbon to burning in the drained areas increased ninefold.
“Even though the organic matter accumulation doubled over two decades after drainage, severe burning triggered the complete loss of this newly stored carbon, plus a further 450 years’ worth of peat accumulation,” Donahue said.
This study — along with the earlier work on peatlands and tundra — provides yet more evidence that the carbon cycle has a point of no return beyond which it becomes all but impossible to stop catastrophic global warming — the point at which we start to lose carbon rapidly from the northern peatlands and the permafrost (see Tundra, Part 2: The point of no return).
Again, the people out there who think R&D or an energy quest is going to stop us from multiple catastrophes are deluding themselves and others. We need to start aggressive mitigation now as every major independent study concludes — see Study Confirms Optimal Climate Strategy: Deploy, Deploy, Deploy, Research and Develop, Deploy, Deploy, Deploy.
Related posts and amplifying feedbacks:
- Journal of Climate: New cloud feedback results “provide support for the high end of current estimates of global climate sensitivity”
- The destruction of the tropical wetlands
- Decelerating growth in tropical forest trees — thanks to accelerating carbon dioxide
- Wildfires and Climate-Driven forest destruction by pests
- The desertification-global warming feedback
- Greenland Ice Sheet “Could Undergo a Self-Amplifying Cycle of Melting and Warming … Difficult to Halt,” Scientists Find
- Science: Vast East Siberian Arctic Shelf methane stores destabilizing and venting: NSF issues world a wake-up call: “Release of even a fraction of the methane stored in the shelf could trigger abrupt climate warming.” Methane and carbon release from the Arctic is the most dangerous amplifying feedback in the entire carbon cycle. This research finds a key “lid” on “the large sub-sea permafrost carbon reservoir” near Eastern Siberia “is clearly perforated, and sedimentary CH4 [methane] is escaping to the atmosphere.”