The terrain in the Arctic has been greening for decades as climate change produces longer and warmer growing seasons for Arctic tundra, previously frozen in permanent permafrost. It now appears that the climate in the Arctic is warming at twice the rate of the rest of the globe. The Arctic tundra permafrost keeps sequestered massive volumes of the greenhouse gas carbon dioxide (carbon) that was captured and sequestered (stored) during during earlier natural, non-anthropogenic (not man-caused), global warming cycles. As the permafrost thaws in warmer climate conditions, this carbon is released as carbon emissions into the atmosphere. At the same time, the new greening Arctic tundra growing seasons create more plant life that captures carbon from the atmosphere in the plant respiration cycle when photosynthates combine with oxygen. The question posed by Assistant Scientist Sue Natali and her team was: Is there a greater net gain of captured carbon during respiration or a net loss of carbon released by thawing permafrost? In the study “Permafrost degradation stimulates carbon loss from experimentally warmed tundra,” published in Ecology, Natali and her team examines the balance between captured carbon and released carbon and discovers that thawing permafrost causes a carbon imbalance that triggers a feedback loop that further increases climate warming and global climate change.
The tundra permafrost store of carbon is comparable to the amount of carbon stored in boreal forests–which comprises an active carbon sink of trees, soil and its own permafrost–and 3 to 7 times the amount of carbon stored in the active tropical forest sinks. When permafrost thaws, the amounts of carbon (carbon dioxide) and methane–from microbes in permafrost–released into the atmosphere trigger a feedback loop that furthers climate change by adding to the warming greenhouse gases. The effects of this looping feedback (warming-carbon emission-warming), which increases atmospheric carbon and methane, is to exacerbate overall global climate change. Natali’s study confirms that permafrost degradation (thaw) doubles annual carbon emissions (or losses of sequestered carbon from thawing permafrost). Even though carbon uptake capture through photosynthesis increases during the elongated warmer growing season, winter vegetation and microbe respiration is also increased, which explains the doubling of annual carbon loss of previously sequestered carbon. Therefore, growing season gains in captured and stored carbon do not offset annual carbon emissions resulting from permafrost thaw releasing stores of sequestered carbon from previously frozen tundra.
As Natli explains, their study simultaneously examined “warming effects on both vegetation and permafrost carbon simultaneously.” This simultaneity is significant because, while growing seasons capture carbon in vegetation, sequestered carbon is lost from thawed permafrost carbon stores, with carbon respiration then continuing through the winter months. Natli’s three-year Arctic field CiPEHR project (Carbon in Permafrost Experimental Heating Research) simulated permafrost degradation within whole-ecosystem Arctic warming. The measurements aimed at determining net gains and losses from the opposing actions of carbon gains through carbon capture resulting from plant growth and carbon losses through carbon emissions resulting from permafrost thaw. The result of the study was that net gains of carbon uptake do not offset net losses of carbon emissions. The data collected leads to increased understanding of permafrost feedbacks and the study results lead to the conclusion that permafrost thaw exacerbates climate change by increasing global warming greenhouse gasses.
Climate change models yield the estimate that permafrost will decline between 30% and 70% within the next one hundred years. These estimates are based on a limited understanding of exactly how much carbon is stored in permafrost and of the rate of release that can be expected. A further unknown is the impact of the permafrost feedback loop on amplifying release of carbon stores. An illustration of the unknown function of feedbacks is the discovery of feedback loops affecting Arctic glaciers. It was found that glacier melting from warmed air caused surrounding waters to warm when melt-off mixed with ocean water. It was found that a feedback loop was created in which warmed waters unexpectedly melted the undersides of glaciers, an action that radically quickened glacier melting. To apply this to permafrost feedbacks, will it be found that a feedback loop somehow accelerates thaw and release in an unexpected way as happened with glacier melting, and if so, how soon will the 30% to 70% permafrost decline actually occur?
“The only way we can accurately project future climate is to understand the responses of both plants and microbes to a warming climate. This study was the first to simulate whole ecosystem warming in the arctic, including permafrost degradation, similar to what is projected to happen as a result of climate change. There is a strong potential for significant global carbon emissions if rates calculated here become typical for permafrost ecosystems in a warmer world.” (Sue Natali)
The Woods Hole Research Center CiPHER project, headed by Natali, “measured CO2 emissions from permafrost thaw and its impact on the carbon balance on an ecosystem level” as Natli conducted in-the-field experiments for “winter warming” and “summer warming.” Winter warming employed snow packs over permafrost to insulate the ground, such as is naturally occurring in agricultural areas of Siberia, until growing season when the snow packs were fully removed. Summer warming employed greenhouses with open tops that facilitated both for climate control and atmospheric exposure. Two sets of measurements were taken during this experiment. The first set measured the effects of warming on carbon uptake by plants while the second set measured release of carbon and methane from thawing plants and microbes. Natali summarizes projections based on the results of CiPHER:
“There is 100 times more carbon stored belowground than aboveground in the Arctic, …. Given the amount of carbon stored belowground in the Arctic, it is very unlikely that plant growth can ever fully offset carbon losses from permafrost thaw.”
Source : ” Permafrost Thaw Exacerbates Climate Change .” Woods Hole Research Center.
Jeremy Hance. ” Boreal forests contain more carbon than tropical forest per hectare. ” mongabay.com.
” Carbon Sequestration 101 .” NOAA Habitat Conservation, NOAA.
” 2013 Arctic Report Card: Greener Arctic of recent years likely to be the new normal .” NOAA Climate.gov.