Melting Arctic Bogs May Hasten Warming, Study Says
The Arctic is warming at least twice as fast as the rest of the planet, according to a recent assessment by the Arctic Council, an intergovernmental agency of polar nations and native groups. And within the Arctic, there are regions that are warming more intensely than others. Scientists refer to them as hot spots.
"There's a great big hot spot over western Siberia," said Larry Smith, an associate professor of geography at the University of California (UCLA), Los Angeles.
The presence of the western Siberia hotspot concerns Smith. Earlier this year he published results of a study in the journal Science showing that an area known as the West Siberian Lowland is home to the world's largest peatlands.
Peatlands consist of layer upon layer of partially decomposed plant material. They play a crucial role in governing the atmospheric concentration of the greenhouse gases carbon dioxide and methane, Smith said. Increased concentrations of atmospheric greenhouse gases can accelerate global warming.
Healthy peatlands absorb carbon dioxide as new vegetation grows. But as peatlands incompletely break down, they release methane and carbon dioxide into the atmosphere.
Calculations by Smith and his colleagues show that, over the long term, Siberian peatlands currently have absorbed more greenhouse gasses through plant growth and storage than they have released through decomposition. Thus, the peatlands currently absorb more carbon dioxide than they release.
However, if temperatures in western Siberia continue to rise, its peatlands could thaw and dry out. They would then essentially become giant compost heaps and begin to release vast amounts of carbon dioxide. This could potentially cause a slight acceleration of global warming, Smith said.
Brenda Ekwurzel is a climate scientist with the Union of Concerned Scientists in Washington, D.C. She said the West Siberian Lowland indeed falls within a hot spot but added that whether thawing peatlands will accelerate global warming remains an open question.
Ekwurzel noted, for example, that while the peatlands have the potential to release large quantities of carbon dioxide and methane, changes in the soil and groundwater could lead to increased tree growth, which acts as a carbon sink.
"If it turns out the net impact is increased carbon dioxide and methane emissions to the atmosphere, this would lead to warming and subsequent feedback or amplification cycles," she said.
The Union of Concerned Scientists released in 1999 and updated in 2003 a global map, "Global Warming: Early Warning Signs," that shows regions of the world already experiencing the impacts of climate change.
Ekwurzel said the warming hot spots are usually found in locations where physical responses feed back on each other and amplify a warming trend. Such areas exist in Arctic regions where temperatures are warm enough to melt snow and ice.
In the Arctic white snow and ice reflect 85 to 90 percent of the energy from sunlight, keeping temperatures cool. But as Arctic snow and ice melt, dark ground and ocean waters are exposed. These absorb most of the sunlight's energy, causing a rise in temperature.
"The warming promotes more snow and ice melt, leading to an amplified warming cycle," Ekwurzel said.
An international team of scientists produced the Arctic Climate Impact Assessment, which was released by the Arctic Council on November 8. The assessment found that temperatures in the Arctic rose, on average, twice as fast as the global average temperature rise of 1 degree Fahrenheit (0.6 degree Celsius) between 1954 and 2003.
However, some regions of the Arctic are currently warming faster than others. The assessment found, for example, that northern North America and Siberia have warmed 3.6 to 5.4 degrees Fahrenheit (2 to 3 degrees Celsius) in the past 50 years. by contrast, southern Greenland actually cooled by 1.8 degrees Fahrenheit (1 degree Celsius).
Mark Serreze, an expert on Arctic warming at the University of Colorado at Boulder, said northern North America and western Siberia have experienced greater warming in response to a change in the atmospheric circulation pattern known the Arctic or North Atlantic Oscillation.
"Since the early 1970s it has shifted from a primarily negative mode to a primarily positive mode. … this changes patterns of wind which transport heat," he said.
The changed pattern has resulted in warmer winds blowing over western Siberia and northern North America. This variation in the wind patterns occurs in the background of a general Arctic warming trend, Serreze said.
Smith, the UCLA geographer, is now trying to determine what will happen in western Siberia if temperatures continue to rise, causing the currently frozen peatlands there to thaw and dry out.
Such a scenario would certainly cause the peatlands to decompose and release vast amounts of the carbon dioxide that has been accumulating for the last 11,500 years. However, peat cores taken throughout the region show no evidence for such catastrophic warming in the past, despite evidence that the peat has previously undergone warming episodes.
"That's why it is such a debate," Smith said.
Ekwurzel, the Union of Concerned Scientists climate expert, said a critical factor in future predictions is the amount of water available to the peatlands.
"Some studies suggest a warming and drying would cause decomposition of organic matter and subsequent carbon dioxide emission to the atmosphere faster than net carbon uptake during photosynthesis," she said. "Other studies suggest a net carbon dioxide uptake will occur under different soil, groundwater, and temperature conditions."
Decomposed peatlands, for example, may become more attractive to trees. As trees take root, they would begin absorbing carbon dioxide, turning the region back into a carbon sink, Smith said.
Serreze, the University of Colorado at Boulder researcher, said that the science is "fuzzy" on whether thawed peatlands in western Siberia would accelerate warming. Any effect would likely pale in comparison to human consumption of oil and coal, fossil fuels that emit large amounts of carbon dioxide when burned, he said.
"There's a lot of talk about these vegetation changes, but I'm not really convinced they are all that important compared to other things," he said. "We are loading the atmosphere with greenhouse gases, and that is the big impact."