New research suggests a slow but significant release of greenhouse gases from the submarine permafrost
PICTURE: ARTISTIC DIAGRAM OF THE SUBSEA AND COASTAL PERMAFROST ECOSYSTEMS THAT THE GENERATION AND RELEASE OF GREEN GAS GASES. View more CREDIT: ORIGINAL ARTWORK, CREATED BY VICTOR OLEG LESHYK AT NORTHERN ARIZONA UNIVERSITY FOR THIS STUDY.
In the far north, the swelling Arctic Ocean inundated large parts of the coastal tundra and steppe ecosystems. Although the seawater was only a few degrees above freezing, it began to thaw the permafrost below, exposing billions of tons of organic matter to microbial degradation. The decomposing organic matter began to produce CO2 and CH4, two of the major greenhouse gases.
Although researchers have studied subsea permfrost degradation for decades, difficulties in collecting measurements and sharing data across international and disciplinary areas have prevented an overall estimate of carbon levels and release rate. A new study led by Ph.D. Candidate Sara Sayedi and lead researcher Dr. Ben Abbott from Brigham Young University (BYU), published in the IOP Publishing Journal Environmental Research Letters, shed light on the climatic feedback of permafrost underwater and generated initial estimates of carbon stocks in the overturning, greenhouse gas release and possible future response of the Underwater permafrost zone.
Sayedi and an international team of 25 permafrost researchers worked under the coordination of the Permafrost Carbon Network (PCN), which is supported by the US National Science Foundation. The researchers combined results from published and unpublished studies to estimate the size of carbon stocks, past and present, and the amount of greenhouse gases it could produce over the next three centuries.
Using a method called expert assessment, which combines several independent plausible values, the researchers estimated that the underwater permafrost region currently captures 60 billion tons of methane and contains 560 billion tons of organic carbon in sediments and soils. As a reference, humans have released a total of around 500 billion tons of carbon into the atmosphere since the industrial revolution. This makes the underwater permafrost carbon stock a potentially huge ecosystem feedback on climate change.
"Underwater permafrost is really unique because it is still responding to dramatic climate change from more than ten thousand years ago," said Sayedi. "In a way, it can give us some insight into the possible response of the permafrost that is thawing today due to human activity."
According to estimates by the Sayedi team, underwater permafrost is already releasing significant amounts of greenhouse gases. However, this publication is primarily due to ancient climate change, rather than current human activity. They estimate that underwater permafrost releases approximately 140 million tons of CO2 and 5.3 million tons of CH4 into the atmosphere every year. This corresponds in size to Spain's entire greenhouse gas footprint.
The researchers found that the release of CH4 and CO2 from underwater permafrost could increase significantly if human-made climate change continues. However, this response is expected to be over the next three centuries and not abruptly. The researchers estimated that the amount of future greenhouse gas release from underwater permafrost is directly related to future human emissions. They found that under a normal scenario, heating the underwater permafrost releases four times more additional CO2 and CH4 than reducing human emissions to keep the warming below 2 ° C.
"These results are important because they indicate significant, but slow, climate feedback," said Sayedi. "Some coverage of this region has indicated that human emissions could trigger a catastrophic release of methane hydrates. However, our study suggests a gradual increase over many decades."
Even if this climate feedback process is relatively gradual, the researchers suggest that underwater permafrost is not included in any current climate agreement or greenhouse gas targets. Sayedi emphasized that there is still a great deal of uncertainty about underwater permafrost and that additional research is needed.
"Compared to how important underwater permafrost could be for future climates, we know shockingly little about this ecosystem," said Sayedi. "We need more sediment and soil samples, as well as a better monitoring network, to determine when greenhouse gas releases are responding to current warming and how quickly this giant carbon pool is awakening from its frozen sleep."
This research was funded by the US National Science Foundation and BYU Graduate Studies.
Summary of the most important scientific points:
The underwater permafrost has been thawing since the end of the last ice age (~ 14,000 years ago) when it was inundated by the ocean. An international team of 25 permafrost researchers estimates that 60 billion tons of methane and 560 billion tons of organic carbon are currently trapped in sediments and soils in the underwater permafrost region. However, the exact amount of these carbon stocks remains highly uncertain. This carbon is already being released from the underwater permafrost region, although it remains unclear whether this is a natural response to deicing or if anthropogenic warming is accelerating the production and release of greenhouse gases, researchers estimate that the underwater permafrost region is currently around 140 million each year Releases tons of CO2 and 5.3 million tons of CH4 into the atmosphere. This represents a small fraction of total anthropogenic greenhouse gas emissions – roughly equal to Spain's greenhouse gas footprint. Experts predict a gradual increase in emissions from underwater permafrost over the next three hundred years, rather than abrupt releases. The amount of greenhouse gas emissions increases depends on how much human emissions are reduced. Experts estimate that around ¾ of the additional underwater emissions can be avoided if humans actively reduce their emissions compared to a scenario without damage limitation. This climate feedback method is still practically missing in the climate policy discussions, and further field observations are required in order to be able to better predict the future of this system.
Quotes from other co-authors:
“I think this study has three important messages. First, underwater permafrost is unlikely to be a climate time bomb on a hair trigger. Second, underwater permafrost is a potentially large climate feedback factor that needs to be considered in climate negotiations. Third, there is still a great deal that we do not know about this system. We really need additional research, including international collaboration between northern countries and research disciplines. "
Dr. Ben Abbott, lead researcher on the project at Brigham Young University
“This work demonstrates the power of science synthesis and networking by bringing together experts from different disciplines to assess our level of knowledge based on currently available observations and models. While scientific work continues to be conducted to test these ideas, the pooling of knowledge with this expert review provides an important foundation for shaping future research on underwater permafrost greenhouse gas emissions. "
Dr. Ted Schuur, senior investigator for the Permafrost Carbon Network at Northern Arizona University
“This expert assessment is a crucial contribution to the scientific literature to expand our knowledge of underwater permafrost and potential greenhouse gas emissions from this previously unexplored pool. By bringing together scientists from different disciplines, institutions and countries, it has become possible to go beyond individual data points or studies and get a much more comprehensive estimate of underwater permafrost. "
Dr. Christina Skull, co-investigator for the Permafrost Carbon Network at Northern Arizona University