(CN) — Scientists researching millennia-old environmental changes still affecting our world today say that the model predicts certain changes over the next three centuries.
Fourteen thousand years ago, the Arctic Ocean swelled and buried coastal lands. Ocean water just a few degrees above the freezing point moved across permafrost, slowly thawing it and exposing billions of tons of organic matter to microbial breakdown. The decomposing organic matter began releasing carbon dioxide and methane, greenhouse gases that are still rising from the waters today.
A new study, led by doctoral candidate Sara Sayedi and senior researcher Dr. Ben Abbott at Brigham Young University published in the journal Environmental Research Letters, sheds light on the subsea permafrost climate feedback, generating the first estimates of circumarctic carbon stocks, greenhouse gas release, and possible future response of the subsea permafrost zone.
Sayedi and an international team of 25 permafrost researchers used a methodology called expert assessment, which combines multiple, independent plausible values to estimate the size of the past and present subsea carbon stock and how much greenhouse gas it might produce over the next three centuries.
They combined findings from published and unpublished studies to estimate that the subsea permafrost region currently traps 60 billion tons of methane and contains 560 billion tons of organic carbon in sediment and soil. For perspective, humans have released a total of about 500 billion tons of carbon into the atmosphere since the Industrial Revolution.
“Subsea permafrost is really unique because it is still responding to a dramatic climate transition from more than 10,000 years ago,” Sayedi said. “In some ways, it can give us a peek into the possible response of permafrost that is thawing today because of human activity.”
The team found that subsea permafrost is already releasing substantial amounts of greenhouse gas. However, this release is mainly due to ancient climate change rather than current human activity. They estimate that subsea permafrost releases approximately 140 million tons of CO2 and 5.3 million tons of methane to the atmosphere each year. This is similar in magnitude to the overall greenhouse gas footprint of Spain.
Under this model, if human-caused climate change continues, the release of methane and CO2 from subsea permafrost could increase substantially. However, this response is expected to occur over the next three centuries rather than abruptly. Researchers estimated that the amount of future greenhouse gas release from subsea permafrost depends directly on future human emissions. They found that under a business-as-usual scenario, warming subsea permafrost releases four times more additional CO2 and methane compared to when human emissions are reduced to keep warming less than 3.6 degrees Fahrenheit above pre-industrial levels.
“I think there are three important messages from this study,” said Abbott. “First, subsea permafrost is probably not a climate time bomb on a hair trigger. Second, subsea permafrost is a potentially large climate feedback that needs to be considered in climate negotiations. Third, there is still a huge amount that we don't know about this system. We really need additional research, including international collaboration across northern countries and research disciplines.”
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