Earth’s land ecosystems are more resilient carbon sinks than previously believed.
Earth’s vast habitats from the poles to the equator have a robust capacity to remove carbon dioxide from the atmosphere due to previously undiscovered rock nitrogen weathering reactions that distribute natural fertilizers around the world.
The new science underscores the importance of preserving these ecosystems and is detailed in a paper published in the journal Global Biogeochemical Cycles by a research team led by Cornell University, Northern Arizona University, and the University of California at Davis.
“Excess carbon is already harming people, economies, and our planet,” said Benjamin Houlton, the paper’s senior author and Cornell’s Dean of the College of Agriculture and Life Sciences. “But we’ve been enjoying a free subsidy provided by Earth – a large carbon sink on land and in the ocean – and, as a society, we’re not paying for the carbon-sink service explicitly. But where is this sink and how long will it last?”
Since the start of the Industrial Revolution, humanity has been pouring carbon dioxide into the atmosphere. However, land and its vegetation have been naturally drawing down nearly a quarter of it. It was only in the late 1990s that scientists discovered this terrestrial carbon sink. With another quarter of the carbon dioxide going into the oceans, the remaining half of the carbon dioxide remains in the atmosphere contributing to climate change.
“We’re facing incredible threats from climate change and unless we find pathways to store and sequester carbon, it will get worse,” Houlton said.
Slow-Release Nitrogen Strengthens Carbon Uptake
Through the rest of the century, background nitrogen inputs from rock weathering and biological fixation can contribute two to five times more to terrestrial carbon uptake than nitrogen pollution primarily from agricultural and industrial activities, said the scientists, looking at a business-as-usual scenario.
“Previously, we had believed that this terrestrial carbon sink was more vulnerable,” said lead author Pawlok Dass, a postdoctoral researcher at Northern Arizona University, formerly in Houlton’s laboratory at the University of California, Davis, where Houlton conducted the research before coming to Cornell. “Now we’re suggesting that because of the previously undiscovered slow-release nitrogen, the terrestrial carbon sink will continue to be robust.”
Still, society should not lower its guard, as fossil fuel use tends to add excess nitrogen to the atmosphere, which instead of acting as a fertilizer, bypasses terrestrial carbon cycles, which in turn, pollutes downstream water bodies. Abating such excess nitrogen pollution can boost human health, environment, and the economy, Dass said, without jeopardizing the natural, terrestrial carbon sinks.
Conserving Key Ecosystems to Protect Carbon Sinks
Dass explained that to preserve carbon sinks, we need to conserve places where rock nitrogen weathering or biological nitrogen fixation is strong – such as the biologically diverse tropical forests, mountainous regions, and the rapidly changing boreal zone (the entire stretch of forests stretching from Alaska to Canada to Siberia, for example).
“Our work suggests that the conservation of these ecosystems, which have built-in capacity to absorb carbon dioxide,” Houlton said, “is going to be vital to making sure that we don’t lose out on Earth’s terrestrial carbon sink service in the future.”
Reference: “Bedrock Weathering Controls on Terrestrial Carbon-Nitrogen-Climate Interactions” by Pawlok Dass, Benjamin Z. Houlton, Yingping Wang, David Wårlind and Scott Morford, 17 August 2021, Global Biogeochemical Cycles.
DOI: 10.1029/2020GB006933
Funding for this research was provided by the NSF.
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2 Comments
“Since the start of the Industrial Revolution, humanity has been pouring carbon dioxide into the atmosphere. However, land and its vegetation has been naturally drawing down nearly a quarter of it. … With another quarter of the carbon dioxide going into the oceans, the remaining half of the carbon dioxide remains in the atmosphere contributing to climate change.”
This is a simplistic and inaccurate representation of the Carbon Cycle. Humans only contribute about 3-5% of the annual carbon flux. While the net increase in the atmospheric CO2 amounts to about half of the total anthropogenic emissions, it is a spurious correlation; it is coincidence. During the height of the pandemic shutdown, there was no measurable change in either the seasonal high or the seasonal rate of growth of CO2. That is because, of the total CO2 flux from all sources, it is sequestered in proportion to the capacity of the sink. The oceans (both source and sink) and the atmosphere can’t tell the difference between anthropogenic sources and natural. There is a continuous exchange between ALL sources and ALL sinks. The seasonality of the growth of atmospheric CO2, with it peaking in May in the northern hemisphere, speaks to its dominantly organic origin. That is, bacterial and fungal decomposition of dead plants during the Winter and early-Spring. Outgassing, from tropical oceans year round, swamps the human production. A warming Earth undoubtedly has increased outgassing, and reduced absorption in sub-Arctic waters. That is not to say that humans don’t contribute to the rise in CO2. However, it is more like 5% than 50%.
“… fossil fuel use tends to add excess nitrogen to the atmosphere, which instead of acting as a fertilizer, bypasses terrestrial carbon cycles, which in turn, pollutes downstream water bodies.”
I suspect that the nitrous oxides resulting from combustion pales in comparison to the made-for-purpose nitrogen fertilizers that have issues with over-application and runoff, and similarly can bypass the Carbon Cycle, except when it promotes algae blooms and then results in increased CO2 when the algae dies in the Winter.