Vast expanses of peat spreads to the far north of our planet, an accumulation of organic matter too wet to decompose. Although peatlands make up only 3 percent of the Earth’s total area, they store a third of its terrestrial carbon. And they worry climatologists: As the Arctic warms, they dry out and release massive amounts of carbon. People are speeding up this process by draining peatlands and turning them into agricultural fields, releasing even more greenhouse gases.
In a recent paper in the review Scientists progress, researchers massively assess the climate effect of agriculture in these regions: by modeling historical land use, they calculated that between 1750 and 2010, cultivated peatlands in the north released 40 billion tonnes of carbon.
“When the bog dries up, that is, people dig drainage ditches to lower the water table of a bog and make it suitable for bog cultivation, the peat soil is aerated and the Aerobic microbial decomposition of organic matter, which needs oxygen, is enhanced resulting in the release of carbon from the peat into the atmosphere, ”wrote lead author Chunjing Qiu, of the French Laboratoire des sciences du climat et de l environment and the University of Paris-Saclay, in an e-mail to WIRED. Any new plant material that grows and dies there will quickly decompose, releasing its carbon, because there is not enough water to slow down the transformation of organic material into CO.2.
Traditionally, climatologists have focused on how much carbon we could lose through deforestation, but have not often studied the effects of turning peatlands into fields. “We haven’t always done a good job of really accounting for the amount of carbon that might be lost from the ground system, ”says soil scientist Maria Strack, who studies peatlands at the University of Waterloo, but was not involved in the research. “Particularly when we convert peatlands to cropland, the size of this soil organic stock is so large that we may have really underestimated the contribution of these soil carbon losses to our greenhouse gas emissions. tight. “
Humanity is therefore in the process of transforming a critical carbon sink into a source emissions. There are, of course, social drivers underlying this conversion: As the population continues to grow, nations must feed more people with the same amount of land. Economically, it makes sense for farmers to convert what were once soggy tracts to cropland. “This creates a fairly fertile soil, but you lose your carbon at the same time,” says biogeochemist Chris Evans of the UK Center for Ecology and Hydrology, who was not involved in the new paper. “Because so much carbon is lost in some of these landscapes, they’re kind of an empty carbon storage unit, really.”
Agricultural processes only accelerate this loss. Plowing the desiccated peat allows more oxygen to enter it, which further encourages the transformation of organic matter into CO2. The responsible microbes will proliferate even more if farmers add fertilizers that provide them with additional nutrients. In a healthy, moist bog, the plant material it produces should remain and, when dead, be reincorporated into the soggy soil, where its carbon will be trapped for perhaps thousands of years. But on a farm, the crops produced by the land are pulled up from the ground and taken away for sale.
Farmers working on actively cultivated peatlands will irrigate it, keeping the soil at least moist enough for plants to grow. But if the earth is later abandoned and left to dry out completely, it will turn into harmful fuel for forest fires. Because peat is concentrated carbon, it burns easily, but not like the massive conflagrations you’ll see in California or Australia. Instead of producing flames, peat smolders, burns deeper underground, and moves sideways across a landscape. Peat fires are so persistent that they can survive underground during the winter when snow falls above, only to reappear when the landscape thaws in the spring. That’s why scientists call them zombie fires. They can release 100 times the amount of carbon that a fire above ground might.
Nature also dries up the peatlands as the northern lands warm rapidly. The Arctic as a whole green as plant species march north due to climate change. Warmer temperatures mean thunderstorms are more and more frequent, providing the sparks to start huge peat fires: by the year 2100, lightning strikes in the far north could double.
It is therefore extremely important to restore peatlands that farmers have already cultivated. “Not only will you reduce your oxidation emissions, but you will also reduce your fire risk,” says Strack.